ARM: dts: msm: Update PWM device node for PM8909

'#pwm-cells' property is missed in PWM device node for PM8909.
PWM controller nodes must specify the number of cells used for the
specifier using the '#pwm-cells' property. Add the '#pwm-cells'
property to PWM device node for PM8909.

CRs-Fixed: 791068
Change-Id: I7f29b392f0f8bcf7adf375e61ac13f128c702e63
Signed-off-by: Tirupathi Reddy <tirupath@codeaurora.org>