The __do_cache_op function operates with a 'chunk' size of one page
but fails to limit the size of the final chunk so as to not exceed
the specified memory region. Fix this.

Cc: <stable@vger.kernel.org>
Reported-by: NChristian Gmeiner <christian.gmeiner@gmail.com>
Tested-by: NChristian Gmeiner <christian.gmeiner@gmail.com>
Acked-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NJon Medhurst <tixy@linaro.org>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>