media: dvb-core: remove variable n, turn for-loop to while-loop

Variable n is just being incremented and it's never used
anywhere else. The variable and the increment are redundant so
remove it. This allows the for-loop to be replaced with a
while-loop.

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Reviewed-by: Tommaso Merciai <tommaso.merciai@amarulasolutions.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>