media: tda7432: fix spelling mistake "maximium" -> "maximum"

There is a spelling mistake in the module description as well
as a comment. Fix them.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>