pwm: qpnp: Allocate the base for pwm chip automatically

Currently we're setting the base of a pwm chip with the channel number
while adding the pwm chip. Generic pwm driver maintains a single
bitmap for the channels from multiple devices. If there are multiple
PWM hardware blocks with the same channel number, this causes a
probe failure for the second device as that base is allocated already
for the first device. Fix that by setting the base to be allocated
automatically.

Change-Id: If533ab0e70b5e32adac9ab53efdb6cd30edacadb
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>