hwrng: omap - Fix included header from 'asm'

This commit fixes the checkpatch warning:
WARNING: Use #include <linux/io.h> instead of <asm/io.h>
drivers/char/hw_random/omap-rng.c:34
Signed-off-by: Tian Tao <tiantao6@hisilicon.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/char/hw_random/omap-rng.c

@@ -30,8 +30,7 @@
 #include <linux/of_address.h>
 #include <linux/interrupt.h>
 #include <linux/clk.h>
-
-#include <asm/io.h>
+#include <linux/io.h>
 
 #define RNG_REG_STATUS_RDY			(1 << 0)