f2fs: introduce f2fs_kmalloc to wrap kmalloc

This patch adds f2fs_kmalloc.

Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index 19e9faf..38d56f6 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -96,7 +96,7 @@
 	dev_t dev = sbi->sb->s_bdev->bd_dev;
 	int err = 0;
 
-	gc_th = kmalloc(sizeof(struct f2fs_gc_kthread), GFP_KERNEL);
+	gc_th = f2fs_kmalloc(sizeof(struct f2fs_gc_kthread), GFP_KERNEL);
 	if (!gc_th) {
 		err = -ENOMEM;
 		goto out;