[ARM] 3389/1: typo and grammar fix

Patch from Erik Hovland

I found a typo and what seems to be a run-on sentence in
arch/arm/common/dmabounce.c

This patch corrects both.

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