init: fix copying boot properties

The previous patch "init: verify size of property buffers passed
to property_get" incorrectly modified one of the callers,
resulting in ro.serialno, ro.bootmode, ro.baseband, and
ro.bootloader always being set to their default values.

Bug: 9469860
Change-Id: Id45bd8dd657e8d61f4cfaf7e6b2559d2bfd05181