tests: drivers: spi: Correct the spi node for ek_ra8d1

Currently, the SPI pinctrl is incorrect for the spi0 node.
In this PR (#77850), we changed the pinctrl number for SPI
from spi0 to spi1, but we forgot to update the node name
to spi1.
This commit aims to:
- Correct the spi node in test app spi_loopback for ek_ra8d1

Signed-off-by: Khoa Nguyen <khoa.nguyen.xh@renesas.com>

tests/drivers/spi/spi_loopback/boards/ek_ra8d1.overlay

@@ -1,9 +1,9 @@
 /*
- * Copyright (c) 2024 Renesas Electronics Corporation
+ * Copyright (c) 2024-2025 Renesas Electronics Corporation
  * SPDX-License-Identifier: Apache-2.0
  */
 
-&spi0 {
+&spi1 {
 	rx-dtc;
 	tx-dtc;
 	slow@0 {