ARM: dts: msm: Correct the WLED string configuration for SM6150

SM6150 platform has WLED strings 1 and 2 connected, instead of the
current configuration of 1, 2 and 3. Fix this.

Change-Id: I3fe12c8901607387e1230043bd6d39ecb0c6eb0f
Signed-off-by: Kiran Gunda <kgunda@codeaurora.org>