phy: qcom-qusb2: Fix crash if nvmem cell not specified
Driver currently crashes due to NULL pointer deference
while updating PHY tune register if nvmem cell is NULL.
Since, fused value for Tune1/2 register is optional,
we'd rather bail out.
Fixes: ca04d9d3e1b1 ("phy: qcom-qusb2: New driver for QUSB2 PHY on Qcom chips") Reviewed-by: Vivek Gautam <vivek.gautam@codeaurora.org> Reviewed-by: Evan Green <evgreen@chromium.org> Cc: stable <stable@vger.kernel.org> # 4.14+ Signed-off-by: Manu Gautam <mgautam@codeaurora.org> Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>