omfs: fix potential integer overflow in allocator

Both 'i' and 'bits_per_entry' are signed integers but the result is a
u64 block number.  Cast i to u64 to avoid truncation on 32-bit targets.

Found by Coverity (CID 200679).
Signed-off-by: Bob Copeland <me@bobcopeland.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/omfs/bitmap.c

@@ -159,7 +159,7 @@ int omfs_allocate_range(struct super_block *sb,
 	goto out;
 
 found:
-	*return_block = i * bits_per_entry + bit;
+	*return_block = (u64) i * bits_per_entry + bit;
 	*return_size = run;
 	ret = set_run(sb, i, bits_per_entry, bit, run, 1);