mmc: sdhci-s3c: pass IRQF ONESHOT to request threaded irq

Fix a boot regression in existing kernels causing:

genirq: Threaded irq requested with handler=NULL and !ONESHOT for irq XXX

caused by 1c6c6952 (genirq: Reject bogus threaded irq requests).

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Chris Ball <cjb@laptop.org>