riscv: alternatives: move length validation inside the subsection

[Changbin Du <changbin.du@huawei.com>]

Apply the same fix from commit 966a0acce2fc ("arm64/alternatives: move
length validation inside the subsection") to riscv.  Due to the one-pass
design of LLVM's integrated assembler, it can not compute the length of
instructions if the .org directive is outside of the subsection that these
instructions are in.

Here is the build error reported by llvm:

In file included from ./arch/riscv/include/asm/pgtable.h:108:
./arch/riscv/include/asm/tlbflush.h:23:2: error: expected assembly-time absolute expression
        ALT_FLUSH_TLB_PAGE(__asm__ __volatile__ ("sfence.vma %0" : : "r" (addr) : "memory"));
        ^
./arch/riscv/include/asm/errata_list.h:41:5: note: expanded from macro 'ALT_FLUSH_TLB_PAGE'
asm(ALTERNATIVE("sfence.vma %0", "sfence.vma", SIFIVE_VENDOR_ID,        \
    ^
./arch/riscv/include/asm/alternative-macros.h:187:2: note: expanded from macro 'ALTERNATIVE'
        _ALTERNATIVE_CFG(old_content, new_content, vendor_id, errata_id, CONFIG_k)
        ^
./arch/riscv/include/asm/alternative-macros.h:113:2: note: expanded from macro '_ALTERNATIVE_CFG'
        __ALTERNATIVE_CFG(old_c, new_c, vendor_id, errata_id, IS_ENABLED(CONFIG_k))
        ^
./arch/riscv/include/asm/alternative-macros.h:110:2: note: expanded from macro '__ALTERNATIVE_CFG'
        ALT_NEW_CONTENT(vendor_id, errata_id, enable, new_c)
        ^
./arch/riscv/include/asm/alternative-macros.h:98:3: note: expanded from macro 'ALT_NEW_CONTENT'
        ".org   . - (887b - 886b) + (889b - 888b)\n"                    \
         ^
<inline asm>:25:6: note: instantiated into assembly here
.org    . - (887b - 886b) + (889b - 888b)
        ^

Signed-off-by: Changbin Du <changbin.du@gmail.com>
---
 arch/riscv/include/asm/alternative-macros.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/riscv/include/asm/alternative-macros.h b/arch/riscv/include/asm/alternative-macros.h
index e13b1f6bb400..c7d7f1945768 100644
--- a/arch/riscv/include/asm/alternative-macros.h
+++ b/arch/riscv/include/asm/alternative-macros.h
@@ -94,9 +94,9 @@
 	new_c "\n"							\
 	".option pop\n"							\
 	"889 :\n"							\
-	".previous\n"							\
 	".org	. - (887b - 886b) + (889b - 888b)\n"			\
 	".org	. - (889b - 888b) + (887b - 886b)\n"			\
+	".previous\n"							\
 	".endif\n"
 
 #define __ALTERNATIVE_CFG(old_c, new_c, vendor_id, errata_id, enable)	\
-- 
2.26.2