can: flexcan: Use devm_ioremap_resource()

Using devm_ioremap_resource() can make the code simpler and smaller.

Also, place alloc_candev() after of_match_device() to make error handling
easier.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>