mmc: omap_hsmmc: consolidate flush posted writes for HSMMC IRQs

Flushing spurious IRQs from HSMMC IP is done twice in omap_hsmmc_irq
and omap_hsmmc_do_irq.  Consolidate them to one location.

Signed-off-by: Venkatraman S <svenkatr@ti.com>
Acked-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Chris Ball <cjb@laptop.org>