sh: Force __access_ok() to obey address space limit.

When the thread_info->addr_limit changes were introduced, __access_ok()
was missed in the conversion, allowing user processes to perform P1/P2
accesses under certain conditions.

This has already been corrected with the nommu refactoring in later
kernels.

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