ARM: 7650/1: mm: replace direct access to mm->context.id with new macro

The mmid macro is meant to be used to get the mm->context.id data
from the mm structure, but it seems to have been missed in a cuple
of files.

Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>