leds: qti-flash: Add new compatible string for pm2250 flash

PM2250 supports a single flash channel. Add "qcom,pm2250-flash-led"
compatible string to enable the support for PM2250 flash/torch.

Change-Id: I125824b5e85cf0bfed4a1c3d855c45210d03826d
Signed-off-by: Kiran Gunda <kgunda@codeaurora.org>