spi: spi-imx: Add check for spi_imx_setupxfer()

spi: spi-imx: Add check for spi_imx_setupxfer()

Add check for the return value of spi_imx_setupxfer().
spi_imx->rx and spi_imx->tx function pointer can be NULL when
spi_imx_setupxfer() return error, and make NULL pointer dereference.

 Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
 Call trace:
  0x0
  spi_imx_pio_transfer+0x50/0xd8
  spi_imx_transfer_one+0x18c/0x858
  spi_transfer_one_message+0x43c/0x790
  __spi_pump_transfer_message+0x238/0x5d4
  __spi_sync+0x2b0/0x454
  spi_write_then_read+0x11c/0x200

Signed-off-by: Tamura Dai <kirinode0@gmail.com>
Reviewed-by: Carlos Song <carlos.song@nxp.com>
Link: https://patch.msgid.link/20250417011700.14436-1-kirinode0@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>