f2fs: avoid returning uninitialized value to userspace from f2fs_trim_fs()

If user specifies too low end sector for trimming, f2fs_trim_fs() will
use uninitialized value as a number of trimmed blocks and returns it to
userspace. Initialize number of trimmed blocks early to avoid the
problem.

Coverity-id: 1248809
CC: stable@vger.kernel.org
Signed-off-by: NJan Kara <jack@suse.cz>
Signed-off-by: NJaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/segment.c

@@ -1032,6 +1032,7 @@ int f2fs_trim_fs(struct f2fs_sb_info *sbi, struct fstrim_range *range)
 						range->len < sbi->blocksize)
 		return -EINVAL;
 
+	cpc.trimmed = 0;
 	if (end <= MAIN_BLKADDR(sbi))
 		goto out;
 
@@ -1043,7 +1044,6 @@ int f2fs_trim_fs(struct f2fs_sb_info *sbi, struct fstrim_range *range)
 	cpc.trim_start = start_segno;
 	cpc.trim_end = end_segno;
 	cpc.trim_minlen = range->minlen >> sbi->log_blocksize;
-	cpc.trimmed = 0;
 
 	/* do checkpoint to issue discard commands safely */
 	write_checkpoint(sbi, &cpc);