can: flexcan: use devm_platform_ioremap_resource() to simplify code

Use the new helper devm_platform_ioremap_resource() which wraps the
platform_get_resource() and devm_ioremap_resource() together to simplify
the code.

Signed-off-by: Joakim Zhang <qiangqing.zhang@nxp.com>
Reviewed-by: Sean Nyekjaer <sean@geanix.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>