media: dvb-usb: dib0700_devices: Add missing release_firmware()

Add missing release_firmware on the error paths.

drivers/media/usb/dvb-usb/dib0700_devices.c:2415 stk9090m_frontend_attach() warn: 'state->frontend_firmware' from request_firmware() not released on lines: 2415.
drivers/media/usb/dvb-usb/dib0700_devices.c:2497 nim9090md_frontend_attach() warn: 'state->frontend_firmware' from request_firmware() not released on lines: 2489,2497.

Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>