spi: spi-mxs: Remove unneeded check for platform_get_resource()

As devm_ioremap_resource() is used on probe, there is no need to explicitly
check the return value from platform_get_resource(), as this is something that
devm_ioremap_resource() takes care by itself.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Mark Brown <broonie@linaro.org>