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>