xfs: reorganize xfs_iomap_prealloc_size to remove indentation

The majority of xfs_iomap_prealloc_size() executes within the
check for lack of default I/O size. Reverse the logic to remove the
extra indentation.
Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Ben Myers <bpm@sgi.com>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>

fs/xfs/xfs_iomap.c

@@ -381,12 +381,13 @@ xfs_iomap_prealloc_size(
 	int			nimaps)
 {
 	xfs_fsblock_t		alloc_blocks = 0;
+	int			shift = 0;
+	int64_t			freesp;
 
 	alloc_blocks = xfs_iomap_eof_prealloc_initial_size(mp, ip, offset,
 							   imap, nimaps);
-	if (alloc_blocks > 0) {
-		int shift = 0;
-		int64_t freesp;
+	if (!alloc_blocks)
+		goto check_writeio;
 
 	alloc_blocks = XFS_FILEOFF_MIN(MAXEXTLEN,
 				rounddown_pow_of_two(alloc_blocks));
@@ -415,8 +416,8 @@ xfs_iomap_prealloc_size(
 	 */
 	while (alloc_blocks && alloc_blocks >= freesp)
 		alloc_blocks >>= 4;
-	}
 
+check_writeio:
 	if (alloc_blocks < mp->m_writeio_blocks)
 		alloc_blocks = mp->m_writeio_blocks;