ARM: dts: msm: add sync write delay of WLED for QRD8917

Add DT property for sync write delay for WLED module, which is needed
between two consecutive sync register writes, for MSM8917 QRD that
uses PMI8937.

Change-Id: Iab8096d7baedfae258fdad0dcdb8007bee747cc3
Signed-off-by: Mao Li <maol@codeaurora.org>