drivers: spi: fix return value of spi_transceive for STM32 slaves
drivers: spi: fix return value of spi_transceive for STM32 slaves

Return correctly the number of received bytes for a
spi_transceive on a STM32 SPI slave.
Fixes #52216

Signed-off-by: Benedikt Schmidt <15c2bbfe1d8dcfe05fdbc9b78c35d10937b406a6@embedded-solutions.at>
zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr