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
Signed-off-by: Akhil P Oommen <akhilpo@codeaurora.org>
Link: https://lore.kernel.org/r/20211118154903.2.I3ae019673a0cc45d83a193a7858748dd03dbb820@changeidSigned-off-by: Rob Clark <robdclark@chromium.org>

drivers/gpu/drm/msm/msm_gem_submit.c

@@ -772,6 +772,7 @@ int msm_ioctl_gem_submit(struct drm_device *dev, void *data,
 		args->nr_cmds);
 	if (IS_ERR(submit)) {
 		ret = PTR_ERR(submit);
+		submit = NULL;
 		goto out_unlock;
 	}