leds: leds-qpnp: Fix using deprecated APIs for getting PWM device

Currently qpnp led driver is using pwm_request() to get the PWM
device for the required channel. Given that we've multiple hardware
blocks supporting PWM channels, using pwm_request which itself is
deprecated will cause problems. Hence switch using to of_pwm_get()
which will get the device based on phandle specified in device tree.

In addition, redundant pwm-channel information is not required for
led devices as they only need the PWM device to configure the period
and duty cycle of the required channel. Hence remove the pwm-channel
entry in pwm_config_data of led device. Also replace the pwm-channel
defined for led devices with the phandle of pwm devices in DT.

Change-Id: If626594214e7eab4bfb3a19bf515ff28661c4c8d
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>