[media] dib8000: Fix a few warnings when compiled for avr32

	drivers/media/dvb-frontends/dib8000.c: In function 'dib8000_get_time_us':
	drivers/media/dvb-frontends/dib8000.c:3957: warning: 'interleaving' may be used uninitialized in this function
	drivers/media/dvb-frontends/dib8000.c:3956: warning: 'rate_denum' may be used uninitialized in this function

Those are actually false positives, but it doesn't hurt cleaning them.

Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>