reset: socfpga: fix for 64-bit compilation

The SoCFPGA Stratix10 reset controller has 32-bit registers. Thus, we
cannot use BITS_PER_LONG in computing the register and bit offset. Instead,
we should be using the width of the hardware register for the calculation.

Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>