[ARM] S3C64XX: Fix EINT group macro definition

Fix IRQ_EINT_GROUP which has an extra _ in it and
an error in the IRQ offset.

Signed-off-by: Matt Hsu <matt_hsu@openmoko.org>
[ben-linux@fluff.org: rewrite description]
Signed-off-by: Ben Dooks <ben-linux@fluff.org>