Input: zforce_ts - stop treating VDD regulator as optional

Input: zforce_ts - stop treating VDD regulator as optional

This regulator is not optional from the controller point of view,
so stop treating it as such. For hard-wired designs that omit the
regulator from their device trees regulator subsystem will create
a dummy instance.

This may introduce unnecessary delay of 100us in case of dummy
regulator, but if it is important the driver should be marked as
using asynchronous probing to avoid even longer delays waiting for
the command completions.

Also use usleep_range() instead of udelay() to avoid spinning.

Tested-by: Andreas Kemnade <andreas@kemnade.info> # Tolino Shine2HD
Link: https://lore.kernel.org/r/20240824055047.1706392-15-dmitry.torokhov@gmail.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>