drm/amdgpu: debugfs: fix NULL dereference in ta_if_invoke_debugfs_write()

If the kzalloc() fails then this code will crash.  Return -ENOMEM instead.

Fixes: e50d9ba0 ("drm/amdgpu: Add debugfs TA load/unload/invoke support")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_psp_ta.c

@@ -254,7 +254,7 @@ static ssize_t ta_if_invoke_debugfs_write(struct file *fp, const char *buf, size
 
 	shared_buf = kzalloc(shared_buf_len, GFP_KERNEL);
 	if (!shared_buf)
-		ret = -ENOMEM;
+		return -ENOMEM;
 	if (copy_from_user((void *)shared_buf, &buf[copy_pos], shared_buf_len)) {
 		ret = -EFAULT;
 		goto err_free_shared_buf;