[MMC] au1xmmc: Fix a compilation warning ('status' is not used)

Fix a trivial compilation warning:

  CC      drivers/mmc/au1xmmc.o
drivers/mmc/au1xmmc.c: In function ‘au1xmmc_dma_callback’:
drivers/mmc/au1xmmc.c:743: warning: unused variable ‘status’

Signed-off-by: Martin Michlmayr <tbm@cyrius.com>
Acked-by: Martin Michlmayr <tbm@cyrius.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>