ARM: dts: msm: Change pwm peroid value for WLED backlight

Currently WLED backlight is configured in 6 bit pwm mode.
Change the pwm period to configure 9 bit pwm mode for better
pwm resolution support. Also remove the min brightness constraint
to put into min brightness level.

CRs-Fixed: 502742
Change-Id: I99b070a35a3000e729de3c5a6e6abb577ac63837
Signed-off-by: Prasad Sodagudi <psodagud@codeaurora.org>