mmc: protect the tmio_mmc driver against a theoretical race

The MMC subsystem does not guarantee, that host driver .request() and
.set_ios() callbacks are serialised. Such concurrent calls, however,
do not have to be meaningfully supported, drivers just have to make
sure to avoid any severe problems.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Chris Ball <cjb@laptop.org>
diff --git a/drivers/mmc/host/tmio_mmc.h b/drivers/mmc/host/tmio_mmc.h
index c1470e6..58138a2 100644
--- a/drivers/mmc/host/tmio_mmc.h
+++ b/drivers/mmc/host/tmio_mmc.h
@@ -19,6 +19,7 @@
 #include <linux/highmem.h>
 #include <linux/mmc/tmio.h>
 #include <linux/pagemap.h>
+#include <linux/spinlock.h>
 
 /* Definitions for values the CTRL_SDIO_STATUS register can take. */
 #define TMIO_SDIO_STAT_IOIRQ	0x0001