libertas: make lbs_init_mesh() void

Fix the following coccicheck warning:

drivers/net/wireless/marvell/libertas/mesh.c:833:5-8: Unneeded variable:
"ret". Return "0" on line 874

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Jason Yan <yanaijie@huawei.com>
Reviewed-by: Lubomir Rintel <lkundrak@v3.sk>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200410090942.27239-1-yanaijie@huawei.com