[ARM] pxa: remove useless pxa_pm_finish() function

pxa_pm_finish() does nothing but return zero.  The core code
does nothing with this return value, and will not try to call
the finish method in the pm_ops structure if it is NULL.

Therefore, we can remove this useless function.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>