reset: check return value of reset_controller_register()

Currently, reset_controller_register() always return 0, but it would
be better to check its return code.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Sören Brinkmann <soren.brinkmann@xilinx.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>