f2fs: fix to account missing .skipped_gc_rwsem

There is a missing place we forgot to account .skipped_gc_rwsem, fix it.

Fixes: 6f8d4455 ("f2fs: avoid fi->i_gc_rwsem[WRITE] lock in f2fs_gc")
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/gc.c

@@ -1500,8 +1500,10 @@ static int gc_data_segment(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
 			int err;
 
 			if (S_ISREG(inode->i_mode)) {
-				if (!down_write_trylock(&fi->i_gc_rwsem[READ]))
+				if (!down_write_trylock(&fi->i_gc_rwsem[READ])) {
+					sbi->skipped_gc_rwsem++;
 					continue;
+				}
 				if (!down_write_trylock(
 						&fi->i_gc_rwsem[WRITE])) {
 					sbi->skipped_gc_rwsem++;