[ARM] nommu: fix breakage caused by f9720205

Someone forgot to use 'ls include/asm-*/flat.h' or
'grep -r flat_get_addr_from_rp .' to find all architectures which
may be affected by their change.  Fix the fall out.

Noticed-by: Robert P. J. Day <rpjday@crashcourse.ca>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>