[media] technisat-usb2: don't do DMA on the stack

As warned by smatch:
	drivers/media/usb/dvb-usb/technisat-usb2.c:263 technisat_usb2_set_led() error: doing dma on the stack (led)
	drivers/media/usb/dvb-usb/technisat-usb2.c:280 technisat_usb2_set_led_timer() error: doing dma on the stack (&b)
	drivers/media/usb/dvb-usb/technisat-usb2.c:341 technisat_usb2_identify_state() error: doing dma on the stack (version)
	drivers/media/usb/dvb-usb/technisat-usb2.c:609 technisat_usb2_get_ir() error: doing dma on the stack (buf)
	drivers/media/usb/dvb-usb/technisat-usb2.c:619 technisat_usb2_get_ir() error: doing dma on the stack (buf)

Create a buffer at the device state and use it for all the DMA
transfers.

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>