V4L/DVB (11800): tuner-xc2028: show the proper module description for no_poweroff option

There was a typo in the module description for the "no_poweroff" option, where the
help was being associated with the "debug" option instead.

Signed-off-by: Devin Heitmueller <dheitmueller@kernellabs.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>