drm/amdkfd: fix process reference drop on debug ioctl

Prevent dropping the KFD process reference at the end of a debug
IOCTL call where the acquired process value is an error.
Signed-off-by: Jonathan Kim <jonathan.kim@amd.com>
Reviewed-by: Felix Kuehling <felix.kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdkfd/kfd_chardev.c

@@ -2935,6 +2935,7 @@ static int kfd_ioctl_set_debug_trap(struct file *filep, struct kfd_process *p, v
 	if (IS_ERR_OR_NULL(target)) {
 		pr_debug("Cannot find process PID %i to debug\n", args->pid);
 		r = target ? PTR_ERR(target) : -ESRCH;
+		target = NULL;
 		goto out;
 	}