gpu: vga_switcheroo, fix lock imbalance

Stanse found that one error path in vga_switcheroo_debugfs_write omits to
unlock vgasr_mutex.  Fix that.
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/vga/vga_switcheroo.c

@@ -276,8 +276,10 @@ vga_switcheroo_debugfs_write(struct file *filp, const char __user *ubuf,
 
 	mutex_lock(&vgasr_mutex);
 
-	if (!vgasr_priv.active)
-		return -EINVAL;
+	if (!vgasr_priv.active) {
+		cnt = -EINVAL;
+		goto out;
+	}
 
 	/* pwr off the device not in use */
 	if (strncmp(usercmd, "OFF", 3) == 0) {