Change the return type of efi_driver_init() to efi_status_t.

efi_driver_init() calls efi_add_driver() which returns an efi_status_t
value. efi_driver_init() should not subject this value to a conversion to
int losing high bits on 64bit systems.
Signed-off-by: NHeinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: NAlexander Graf <agraf@suse.de>