[PATCH] arm64: Fix calculation of page_offset in case we are running cases other than mem-usage

Patch f49ca13e added '--mem-usage'
support for arm64 architecture.

However, we also need to make sure that the calculation of
'page_offset' is valid in case we are running cases other than
'--mem-usage'.

This patch does the same. I tested this patch on my qualcomm and apm
mustang arm64 boards.

Signed-off-by: Bhupesh Sharma <bhsharma@redhat.com>