phy: qcom-qmp: initialize the pointer to NULL

phy: qcom-qmp: initialize the pointer to NULL

Smatch complains:
drivers/phy/qualcomm/phy-qcom-qmp.c:3899 qcom_qmp_phy_probe() error: uninitialized symbol 'dp_cfg'.
drivers/phy/qualcomm/phy-qcom-qmp.c:3900 qcom_qmp_phy_probe() error: uninitialized symbol 'dp_serdes'.
drivers/phy/qualcomm/phy-qcom-qmp.c:3902 qcom_qmp_phy_probe() error: uninitialized symbol 'usb_cfg'.

This is a warning but not a practical one as dp_cfg, dp_serdes and
usb_cfg will be set and used when valid. So we can set the pointers to
NULL to quiesce the warnings.

Fixes: 52e013d0bffa ("phy: qcom-qmp: Add support for DP in USB3+DP combo phy")
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Link: https://lore.kernel.org/r/20201001070911.140019-1-vkoul@kernel.org
Signed-off-by: Vinod Koul <vkoul@kernel.org>