rpmsg: glink: Add missing MODULE_LICENSE

The qcom_glink_native driver is missing a MODULE_LICENSE(), correct
this.

Fixes: 835764dd ("rpmsg: glink: Move the common glink protocol implementation to glink_native.c")
Cc: stable@vger.kernel.org
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>