remoteproc/mediatek: fix invalid use of sizeof in scp_ipi_init()

remoteproc/mediatek: fix invalid use of sizeof in scp_ipi_init()

sizeof() when applied to a pointer typed expression gives the
size of the pointer, not that of the pointed data.

Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Fixes: 63c13d61eafe ("remoteproc/mediatek: add SCP support for mt8183")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Link: https://lore.kernel.org/r/20200509084237.36293-1-weiyongjun1@huawei.com
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>