arm:i2c: Don't mask return from i2c_recv()

It can't fail, and now that it returns a uint8_t a 0xff mask
is unnecessary.

Signed-off-by: Corey Minyard <cminyard@mvista.com>
Suggested-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>

hw/arm/stellaris.c

@@ -811,7 +811,7 @@ static void stellaris_i2c_write(void *opaque, hwaddr offset,
             /* TODO: Handle errors.  */
             if (s->msa & 1) {
                 /* Recv */
-                s->mdr = i2c_recv(s->bus) & 0xff;
+                s->mdr = i2c_recv(s->bus);
             } else {
                 /* Send */
                 i2c_send(s->bus, s->mdr);