sh64: Fix up PC casting in unaligned fixup notifier with 32bit ABI.

Presently the build bails with the following:

  CC      arch/sh/mm/alignment.o
cc1: warnings being treated as errors
arch/sh/mm/alignment.c: In function 'unaligned_fixups_notify':
arch/sh/mm/alignment.c:69: warning: cast to pointer from integer of different size
arch/sh/mm/alignment.c:74: warning: cast to pointer from integer of different size
make[2]: *** [arch/sh/mm/alignment.o] Error 1

This is due to the fact that regs->pc is always 64-bit, while the pointer size
depends on the ABI. Wrapping through instruction_pointer() takes care of the
appropriate casting for both configurations.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>