crypto: hisilicon/qm - delete redundant null assignment operations

There is no security data in the pointer. It is only a value transferred
as a structure. It makes no sense to zero a variable that is on the stack.
So not need to set the pointer to null.
Signed-off-by: NKai Ye <yekai13@huawei.com>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>

drivers/crypto/hisilicon/qm.c

@@ -1773,7 +1773,6 @@ static void dfx_regs_uninit(struct hisi_qm *qm,
 		dregs[i].regs = NULL;
 	}
 	kfree(dregs);
-	dregs = NULL;
 }
 
 /**