vchiq_arm: Don't free on error

[imp]

Summary

When actual_pages is -1, calling vm_page_unhold_pages will loop
forever. We don't actually need to loop. In fact, it will either be -1
or the right number of pages: we never return a partial allocation. It
might be more proper to assert this, but since this is contrib code,
make a minimal change to avoid the infinite loop.

Sponsored by: Netflix

Test Plan

I have no way of testing this, but the code is clearly wrong when vm_fault_quick_hold_pages returns -1.