sh: Fix page size alignment in __copy_user_page().

SH-3 comes up with the PAGE_SIZE on a misaligned boundary:

arch/sh/mm/copy_page.S: Assembler messages:
arch/sh/mm/copy_page.S:132: Warning: misaligned data

fix it up with explicit alignment.

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