fs: uninline inode_maybe_inc_iversion()

It has many callsites and is large.

   text	   data	    bss	    dec	    hex	filename
  91796	  15984	    512	 108292	  1a704	mm/shmem.o-before
  91180	  15984	    512	 107676	  1a49c	mm/shmem.o-after

Acked-by: Jeff Layton <jlayton@kernel.org>
Cc: Chuck Lever <chuck.lever@oracle.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>