[media] drx-j: make a few functions static

[media] drx-j: make a few functions static

drivers/media/dvb-frontends/drx39xyj/drx_driver.c:181:7: warning: no previous prototype for 'get_scan_context' [-Wmissing-prototypes]
 void *get_scan_context(pdrx_demod_instance_t demod, void *scan_context)

drivers/media/dvb-frontends/drx39xyj/drx_driver.c: At top level:
drivers/media/dvb-frontends/drx39xyj/drx_driver.c:842:5: warning: no previous prototype for 'ctrl_dump_registers' [-Wmissing-prototypes]
 int ctrl_dump_registers(pdrx_demod_instance_t demod,

Acked-by: Devin Heitmueller <dheitmueller@kernellabs.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>