hwmon: qpnp-adc-voltage: Fix ADC channel selection

The AMUX channel numbers are not numbered consequently
after channel number 60. Fix ADC channel selection's
enum index. Channel 4 has been dedicated for USB_ID
now, therefore change the name for clients to easily
identify it.

Change-Id: I7bd58d2ad356541a2122ddf7fe3caa3a37486795
Signed-off-by: Siddartha Mohanadoss <smohanad@codeaurora.org>