f2fs: remove unneeded initialization

No need to initialize  "struct f2fs_gc_kthread *gc_th = NULL",
as gc_th = NULL, will be taken care by the return values of kmalloc().
And fix codes in other places.

Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Amit Sahrawat <a.sahrawat@samsung.com>
diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index 3271be4..644aa38 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -89,7 +89,7 @@
 
 int start_gc_thread(struct f2fs_sb_info *sbi)
 {
-	struct f2fs_gc_kthread *gc_th = NULL;
+	struct f2fs_gc_kthread *gc_th;
 
 	gc_th = kmalloc(sizeof(struct f2fs_gc_kthread), GFP_KERNEL);
 	if (!gc_th)