udf: move calculating of nr_groups into helper function

Signed-off-by: Marcin Slusarz <marcin.slusarz@gmail.com>
Cc: Ben Fennema <bfennema@falcon.csc.calpoly.edu>
Acked-by: Jan Kara <jack@suse.cz>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/udf/balloc.c b/fs/udf/balloc.c
index 8c0c279..3f67d9d 100644
--- a/fs/udf/balloc.c
+++ b/fs/udf/balloc.c
@@ -231,9 +231,7 @@
 		block_count = part_len - first_block;
 
 repeat:
-	nr_groups = (sbi->s_partmaps[partition].s_partition_len +
-		     (sizeof(struct spaceBitmapDesc) << 3) +
-		     (sb->s_blocksize * 8) - 1) / (sb->s_blocksize * 8);
+	nr_groups = udf_compute_nr_groups(sb, partition);
 	block = first_block + (sizeof(struct spaceBitmapDesc) << 3);
 	block_group = block >> (sb->s_blocksize_bits + 3);
 	group_start = block_group ? 0 : sizeof(struct spaceBitmapDesc);