[media] drx-j: prepend function names with drx_ at drx_driver.c

In order to prepare to get rid of drx_driver.c, prepend all functions
there with drx_.

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