spi: spi-zynqmp-gqspi: Fix missing unlock on error in zynqmp_qspi_exec_op()

Add the missing unlock before return from function zynqmp_qspi_exec_op()
in the error handling case.

Fixes: a0f65be6 ("spi: spi-zynqmp-gqspi: add mutex locking for exec_op")
Reported-by: NHulk Robot <hulkci@huawei.com>
Signed-off-by: NWei Yongjun <weiyongjun1@huawei.com>
Link: https://lore.kernel.org/r/20210412160025.194171-1-weiyongjun1@huawei.comSigned-off-by: NMark Brown <broonie@kernel.org>

drivers/spi/spi-zynqmp-gqspi.c

@@ -965,8 +965,10 @@ static int zynqmp_qspi_exec_op(struct spi_mem *mem,
 
 	if (op->cmd.opcode) {
 		tmpbuf = kzalloc(op->cmd.nbytes, GFP_KERNEL | GFP_DMA);
-		if (!tmpbuf)
+		if (!tmpbuf) {
+			mutex_unlock(&xqspi->op_lock);
 			return -ENOMEM;
+		}
 		tmpbuf[0] = op->cmd.opcode;
 		reinit_completion(&xqspi->data_completion);
 		xqspi->txbuf = tmpbuf;