[media] drx-j: remove the useless microcode_size

This var is not used. Remove it from the code, as we'll now be
converting the driver to load the firmware from an external
file.

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