[ARM] 4153/1: fix consistent_sync() off-by-one BUG check

In consistent_sync(), start + size can end up pointing one byte
beyond the end of the direct RAM mapping.  We shouldn't BUG() when
this happens.

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