mmc: omap_hsmmc: clear status flags before starting a new command

Commit 1f6b9fa4 consolidated writes to
the STAT register in one location, moving them from omap_hsmmc_do_irq()
to omap_hsmmc_irq(). This move has the unwanted side effect that the
controller status flags are potentially cleared after a new command has
been started as a consequence of reading the previous status flags.
This means that if the new command changes the status flags before the
IRQ routine returns, those flags may be cleared without handling the
event which asserted them, and thus missing the event.
Move the writing of the STAT register back in omap_hsmmc_do_irq(),
before handling the status flags which generated the interrupt.

Signed-off-by: Francesco Lavra <francescolavra.fl@gmail.com>
Reviewed-and-Tested-by: Balaji T K <balajitk@ti.com>
Signed-off-by: Chris Ball <cjb@laptop.org>