[media] cxusb: Use a dma capable buffer also for reading

Commit 17ce039b4e54 ("[media] cxusb: don't do DMA on stack")
added a kmalloc'ed bounce buffer for writes, but missed to do the same
for reads. As the read only happens after the write is finished, we can
reuse the same buffer.

As dvb_usb_generic_rw handles a read length of 0 by itself, avoid calling
it using the dvb_usb_generic_read wrapper function.

Signed-off-by: Stefan Brüns <stefan.bruens@rwth-aachen.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
static int cxusb_mt352_demod_init(struct dvb_frontend* fe)
{	/* used in both lgz201 and th7579 */
	static u8 clock_config []  = { CLOCK_CTL,  0x38, 0x29 };
	static u8 reset []         = { RESET,      0x80 };
	static u8 adc_ctl_1_cfg [] = { ADC_CTL_1,  0x40 };
	static u8 agc_cfg []       = { AGC_TARGET, 0x24, 0x20 };
	static u8 gpp_ctl_cfg []   = { GPP_CTL,    0x33 };
	static u8 capt_range_cfg[] = { CAPT_RANGE, 0x32 };

	mt352_write(fe, clock_config,   sizeof(clock_config));
	udelay(200);
	mt352_write(fe, reset,          sizeof(reset));
	mt352_write(fe, adc_ctl_1_cfg,  sizeof(adc_ctl_1_cfg));

	mt352_write(fe, agc_cfg,        sizeof(agc_cfg));
	mt352_write(fe, gpp_ctl_cfg,    sizeof(gpp_ctl_cfg));
	mt352_write(fe, capt_range_cfg, sizeof(capt_range_cfg));
	return 0;
}

static int cxusb_mt352_demod_init(struct dvb_frontend* fe)
{	/* used in both lgz201 and th7579 */
	static u8 clock_config []  = { CLOCK_CTL,  0x38, 0x29 };
	static u8 reset []         = { RESET,      0x80 };
	static u8 adc_ctl_1_cfg [] = { ADC_CTL_1,  0x40 };
	static u8 agc_cfg []       = { AGC_TARGET, 0x24, 0x20 };
	static u8 gpp_ctl_cfg []   = { GPP_CTL,    0x33 };
	static u8 capt_range_cfg[] = { CAPT_RANGE, 0x32 };

	mt352_write(fe, clock_config,   sizeof(clock_config));
	udelay(200);
	mt352_write(fe, reset,          sizeof(reset));
	mt352_write(fe, adc_ctl_1_cfg,  sizeof(adc_ctl_1_cfg));

	mt352_write(fe, agc_cfg,        sizeof(agc_cfg));
	mt352_write(fe, gpp_ctl_cfg,    sizeof(gpp_ctl_cfg));
	mt352_write(fe, capt_range_cfg, sizeof(capt_range_cfg));
	return 0;
}
