[ARM] 5411/1: S3C64XX: Fix EINT unmask

Currently the unmask function for EINT interrupts was setting the mask
bit rather than clearing it.  This was also previously reported and
fixed by Kyungmin Park <kyungmin.park@samsung.com> and others.

Acked-By: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>