can: mcp251x: Check return value of spi_setup()

This patch moves setup of SPI bus a bit earlier and adds check for spi_setup()
result to be sure SPI bus is communicating with the device properly.

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Tested-by: Alexander Shiyan <shc_work@mail.ru>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>