rpmsg: glink: add include of header file

With an x86_64 architecture W=1 build, qcom_glink_ssr_notify() is
reported as having no previous prototype.  The prototype is found in
"qcom_glink.h", so we just need "qcom_glink_ssr.c" to include that
file.

Signed-off-by: Alex Elder <elder@linaro.org>
Link: https://lore.kernel.org/r/20210105235528.32538-1-elder@linaro.org


Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>