firmware: qcom: scm: remove unused __qcom_scm_init declaration

__qcom_scm_init has been removed since
commit 9a434cee ("firmware: qcom_scm: Dynamically support
SMCCC and legacy conventions"), so remove it.

Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20220911092912.3219132-1-cuigaosheng1@huawei.com