This patch deletes two calls to smp_mb() that were done after mutex_unlock() 
that contains an implicit memory barrier.

The first one in splice_to_pipe(), where 'do_wakeup' is set to true only if 
pipe->inode is set (and in this case the
if (pipe->inode)
    mutex_unlock(&pipe->inode->i_mutex);
is done too)

The second one in link_pipe(), following inode_double_unlock() that contains 
calls to mutex_unlock() too.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>