V4L/DVB (7377): radio-sf16fmr2.c: fix volume handling

As reported by  Roel Kluin <12o3l@tiscali.nl>:
in drivers/media/radio/radio-sf16fmr2.c:319:

for (i = 0; i < ARRAY_SIZE(radio_qctrl); i++) {
	if ((fmr2->card_type != 11)
        	        && V4L2_CID_AUDIO_VOLUME)
	        radio_qctrl[i].step = 65535;
        ...

I don't understand this '&& V4L2_CID_AUDIO_VOLUME'

While fixing this issue, I've revisited the volume control code and fixed
CodingStyle on the changed procedures.

Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>