Fix attribute names in generated permissions.xml

Previously it would write min_device_sdk whereas the correct name should
be min-device-sdk. This happened for all shared libs attributes.

Test: m nothing
Test: manually installed an apex with a shared lib and made sure PM used
the attributes as expected

Bug: 191978330

Change-Id: Iecf7edd6bae98c7af908d3f320f10ae4973d0396