sdio: add sdio_f0_readb() and sdio_f0_writeb()

Add sdio_f0_readb() and sdio_f0_writeb() functions to reading and
writing function 0 registers.  Writes outside the vendor specific CCCR
registers (0xF0 - 0xFF) are not permitted.

Signed-off-by: David Vrabel <david.vrabel@csr.com>
Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>
diff --git a/include/linux/mmc/sdio_func.h b/include/linux/mmc/sdio_func.h
index f057579..da6a96c 100644
--- a/include/linux/mmc/sdio_func.h
+++ b/include/linux/mmc/sdio_func.h
@@ -141,5 +141,10 @@
 extern int sdio_writesb(struct sdio_func *func, unsigned int addr,
 	void *src, int count);
 
+extern unsigned char sdio_f0_readb(struct sdio_func *func,
+	unsigned int addr, int *err_ret);
+extern void sdio_f0_writeb(struct sdio_func *func, unsigned char b,
+	unsigned int addr, int *err_ret);
+
 #endif