serial: msm-geni-serial: Remove usage of wakeup_source_init API

Remove usage of wakeup_source_init API as the support for this
API is removed in wakeup.c file. Instead use wakeup_source_register
and wakeup_source_unregister APIs.

Change-Id: I0d7f759e6bf0388c713f7ffc4f157e61a25278be
Signed-off-by: Prudhvi Yarlagadda <pyarlaga@codeaurora.org>