drm/msm: Fix dereference of pointer minor before null check

drm/msm: Fix dereference of pointer minor before null check

Currently the pointer minor is being dereferenced before it is null
checked, leading to a potential null pointer dereference issue. Fix this
by dereferencing the pointer only after it has been null checked. Also
Replace minor->dev with dev.

Fixes: 4f89cf40d01e ("drm/msm: bail out late_init_minor() if it is not a GPU device")
Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Reviewed-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
Patchwork: https://patchwork.freedesktop.org/patch/666259/
Signed-off-by: Rob Clark <robin.clark@oss.qualcomm.com>