rpmsg: glink: Add check for kstrdup

Add check for the return value of kstrdup() and return the error
if it fails in order to avoid NULL pointer dereference.

Fixes: b4f8e52b ("rpmsg: Introduce Qualcomm RPM glink driver")
Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn>
Link: https://lore.kernel.org/r/20230619030631.12361-1-jiasheng@iscas.ac.cn


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