mailbox: rockchip: fix a typo in module autoloading

MODULE_DEVICE_TABLE(of, rockchip_mbox_of_match) could let the module
properly autoloaded based on the alias from of_device_id table. It
should be 'rockchip_mbox_of_match' instead of 'rockchp_mbox_of_match',
just fix it.

Fixes: f70ed3b5 ("mailbox: rockchip: Add Rockchip mailbox driver")
Signed-off-by: Liao Chen <liaochen4@huawei.com>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com>