ARM: 8291/1: replace magic number with PAGE_SHIFT macro in fixup_pv code

This line converts PHYS_OFFSET into PHYS_PFN_OFFSET.
It is better to use PAGE_SHIFT rather than the magic number 12.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Acked-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>