staging: imx-drm: remove old FSF address from license text

Linux already includes a copy of the GPL, checkpatch compains about the address.
Remove it from the license text.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>