lightnvm: fix unnecessary NULL check warnings

Remove NULL checks before vfree() to fix these warnings:
./drivers/lightnvm/pblk-gc.c:27:2-7: WARNING: NULL check before some
freeing functions is not needed.
Signed-off-by: Tian Tao <tiantao6@hisilicon.com>
Signed-off-by: Matias Bjørling <matias.bjorling@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/lightnvm/pblk-gc.c

@@ -23,7 +23,6 @@
 
 static void pblk_gc_free_gc_rq(struct pblk_gc_rq *gc_rq)
 {
-	if (gc_rq->data)
 	vfree(gc_rq->data);
 	kfree(gc_rq);
 }