V4L/DVB (5360): Dvb-pll: Use sizeof() to get name length

Better to use sizeof() to get the size of the output buffer for the tuner
name, instead of just hard coding 128.

Signed-off-by: Trent Piepho <xyzzy@speakeasy.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>