hwrng: ba431 - Include kernel.h

There are multiple things in this file that requires kernel.h but
it's only included through other header files indirectly.  This
patch adds a direct inclusion as those indirect inclusions may go
away at any point.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/char/hw_random/ba431-rng.c

@@ -5,6 +5,7 @@
 #include <linux/hw_random.h>
 #include <linux/io.h>
 #include <linux/iopoll.h>
+#include <linux/kernel.h>
 #include <linux/mod_devicetable.h>
 #include <linux/module.h>
 #include <linux/platform_device.h>