x86/kaslr: Drop some redundant checks from __process_mem_region()

Clip the start and end of the region to minimum and mem_limit prior to
the loop. region.start can only increase during the loop, so raising it
to minimum before the loop is enough.

A region that becomes empty due to this will get checked in
the first iteration of the loop.

Drop the check for overlap extending beyond the end of the region. This
will get checked in the next loop iteration anyway.

Rename end to region_end for symmetry with region.start.

Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200728225722.67457-10-nivedita@alum.mit.edu