PXA: Fix warning in zipitz2

Configuring for zipitz2 board...
zipitz2.c: In function ?board_mmc_init?:
zipitz2.c:85:2: warning: implicit declaration of function ?pxa_mmc_register? [-Wimplicit-function-declaration]

---
 board/zipitz2/zipitz2.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

index 4075fb6..82dfa82 100644
@@ -28,6 +28,7 @@
 #include <serial.h>
 #include <asm/arch/hardware.h>
 #include <asm/arch/pxa.h>
+#include <asm/arch/regs-mmc.h>
 #include <spi.h>
 #include <asm/io.h>
 

1.7.9