Return the corresponding error code when first_msi_entry() returns
NULL in mv_xor_v2_probe().

Fixes: 19a340b1 ("dmaengine: mv_xor_v2: new driver")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Link: https://lore.kernel.org/r/20201124010813.1939095-1-chengzhihao1@huawei.comSigned-off-by: Vinod Koul <vkoul@kernel.org>