board: verdin-am62: improve comment on usb phy core voltage

TI recommends to clear the bit independent of the used voltage.
So the comment which claims to do it due to the core voltage
at 0.85V is bogus.

See https://e2e.ti.com/support/processors-group/processors/f/processors-forum/1252724/am625-usb-phy-core-voltage-selection-and-vdda_core_usb-mismatch



Signed-off-by: Max Krummenacher <max.krummenacher@toradex.com>