vidc: Clean up mem_type code

This is redundant.

Signed-off-by: Sultanxda <sultanxda@gmail.com>
mipi_dsi: Clean up panel-voltage interface

*Sysfs variable now reflects the true amount of undervolt
*If an invalid number (ex. not a multiple of 25) is entered then the display will fall back to the previous voltage (after screen is turned off and on, of course)

Signed-off-by: Sultanxda <sultanxda@gmail.com>