Spurious IRQs seen on MMC after 2.6.29.  Flush posted write in IRQ
handler.

The interrupt line is released by clearing the error status bits
in the MMCHS_STAT register, which must occur before the interrupt
handler returns to avoid unwanted irqs.  Hence the need to flush
the posted write.
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>
Signed-off-by: Adrian Hunter <adrian.hunter@nokia.com>
Acked-by: Tony Lindgen <tony@atomide.com>
Signed-off-by: Pierre Ossman <pierre@ossman.eu>