backlight: l4f00242t03: Add check for spi_setup

backlight: l4f00242t03: Add check for spi_setup

Add check for the return value of spi_setup() and return the error
if it fails in order to catch the error.

Signed-off-by: Chen Ni <nichen@iscas.ac.cn>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Link: https://lore.kernel.org/r/20240705092800.3221159-1-nichen@iscas.ac.cn
Signed-off-by: Lee Jones <lee@kernel.org>