[media] rtl28xxu: move usb buffers to state

Buffer needed for USB control message is small so move it to state
and get rid of alloc/free used for each control message.

Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

drivers/media/usb/dvb-usb-v2/rtl28xxu.h

@@ -69,6 +69,7 @@
 
 
 struct rtl28xxu_dev {
+	u8 buf[28];
 	u8 chip_id;
 	u8 tuner;
 	char *tuner_name;