dvb-usb: Don't use stack for reset either

dvb-usb: Don't use stack for reset either

Commit 43fab9793c1f ("[media] dvb-usb: don't use stack for firmware
load") introduced a heap buffer for the firmware writes, but we need
to do the same for the register writes to reset the DVB device's
processor.

Cc: stable@vger.kernel.org # 4.9+
Fixes: 43fab9793c1f ("[media] dvb-usb: don't use stack for firmware load")
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Gbp-Pq: Topic bugfix/all
Gbp-Pq: Name media-dvb-usb-don-t-use-stack-for-reset-either.patch