net: can: mcp251x: propagate the return value of mcp251x_spi_write()

net: can: mcp251x: propagate the return value of mcp251x_spi_write()

Add an integer return value to mcp251x_write_bits() and use it to
propagate the one returned by mcp251x_spi_write(). Return that value on
error in the request() GPIO callback.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Reviewed-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Reviewed-by: Marc Kleine-Budde <mkl@pengutronix.de>
Link: https://patch.msgid.link/20250616-gpiochip-set-rv-net-v2-3-cae0b182a552@linaro.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>