spi: stm32-qspi: Fix stm32_qspi_transfer_one_message() error path

The patch a557fca630cc: "spi: stm32_qspi: Add transfer_one_message()
spi callback" from Aug 23, 2022, leads to the following Smatch static
checker warning:

drivers/spi/spi-stm32-qspi.c:627 stm32_qspi_transfer_one_message()
error: uninitialized symbol 'ret'.Fix the following Smatch static checker warning:

Fixes: a557fca630cc ("spi: stm32_qspi: Add transfer_one_message() spi callback")
Reported-by: Dan Carpenter <[e-mail]>
Signed-off-by: Patrice Chotard <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Mark Brown <[e-mail]>

drivers/spi/spi-stm32-qspi.c

···
 	struct spi_transfer *transfer;
 	struct spi_device *spi = msg->spi;
 	struct spi_mem_op op;
-	int ret;
+	int ret = 0;
 
 	if (!spi->cs_gpiod)
 		return -EOPNOTSUPP;
···
 			dummy_bytes = transfer->len;
 
 			/* if happens, means that message is not correctly built */
-			if (list_is_last(&transfer->transfer_list, &msg->transfers))
+			if (list_is_last(&transfer->transfer_list, &msg->transfers)) {
+				ret = -EINVAL;
 				goto end_of_transfer;
+			}
 
 			transfer = list_next_entry(transfer, transfer_list);
 		}