drm/msm/dp: Add check for null pointer dereferencing

Add check for null returns from functions getting display
property, gpio_config, and wb_cfg.fmt.

CRs-Fixed: 2122564
Change-Id: I2b9124de554c472ca70bcf458be2e030e37adf4c
Signed-off-by: Samantha Tran <samtran@codeaurora.org>
3 files changed