drm/msm: Fix null ptr access msm_ioctl_gem_submit()

In the Linux kernel, the following vulnerability has been resolved:

drm/msm: Fix null ptr access msm_ioctl_gem_submit()

Fix the below null pointer dereference in msm_ioctl_gem_submit():

26545.260705: Call trace:
26545.263223: kref_put+0x1c/0x60
26545.266452: msm_ioctl_gem_submit+0x254/0x744
26545.270937: drm_ioctl_kernel+0xa8/0x124
26545.274976: drm_ioctl+0x21c/0x33c
26545.278478: drm_compat_ioctl+0xdc/0xf0
26545.282428: __arm64_compat_sys_ioctl+0xc8/0x100
26545.287169: el0_svc_common+0xf8/0x250
26545.291025: do_el0_svc_compat+0x28/0x54
26545.295066: el0_svc_compat+0x10/0x1c
26545.298838: el0_sync_compat_handler+0xa8/0xcc
26545.303403: el0_sync_compat+0x188/0x1c0
26545.307445: Code: d503201f d503201f 52800028 4b0803e8 (b8680008)
26545.318799: Kernel panic - not syncing: Oops: Fatal exception