[media] m88ds3103: fix undefined division

[media] m88ds3103: fix undefined division

s32tmp in the below code may be negative, and dev->mclk_khz is an
unsigned type.

	s32tmp = 0x10000 * (tuner_frequency - c->frequency);
	s32tmp = DIV_ROUND_CLOSEST(s32tmp, dev->mclk_khz);

This is undefined, as DIV_ROUND_CLOSEST is undefined for negative
dividends when the divisor is of unsigned type.

So, change mclk_khz to be signed (s32).

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