mmc: at91_mci: add missing linux/highmem.h include

Fix the following error:

at91_mci.c: In function 'at91_mci_sg_to_dma':
at91_mci.c:236: error: implicit declaration of function 'kmap_atomic'
at91_mci.c:236: error: 'KM_BIO_SRC_IRQ' undeclared (first use in this function)
at91_mci.c:236: error: (Each undeclared identifier is reported only once
at91_mci.c:236: error: for each function it appears in.)
at91_mci.c:236: warning: assignment makes pointer from integer without a cast
at91_mci.c:252: error: implicit declaration of function 'kunmap_atomic'
at91_mci.c: In function 'at91_mci_post_dma_read':
at91_mci.c:302: error: 'KM_BIO_SRC_IRQ' undeclared (first use in this function)
at91_mci.c:302: warning: assignment makes pointer from integer without a cast
at91_mci.c:317: error: implicit declaration of function 'flush_kernel_dcache_page'

Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Chris Ball <cjb@laptop.org>
Cc: Nicolas Ferre <nicolas.ferre@atmel.com>
Cc: Andrew Victor <avictor.za@gmail.com>
Cc: Wolfgang Muees <wolfgang.mues@auerswald.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/mmc/host/at91_mci.c

@@ -66,6 +66,7 @@
 #include <linux/clk.h>
 #include <linux/atmel_pdc.h>
 #include <linux/gfp.h>
+#include <linux/highmem.h>
 
 #include <linux/mmc/host.h>