ACPICA: Fix 'may be used uninitialized' warning in acpi_ns_repair_object()

ACPICA: Fix 'may be used uninitialized' warning in acpi_ns_repair_object()

gcc 4.7 warns that new_object may be used uninitialized in this
function.  In fact, all the cases where it's not initialised are
errors that will result in returning early without using it.
Silence the warning by initialising to NULL.

This was done upstream as part of commit d5a36100f62f "ACPICA: Add
mechanism for early object repairs on a per-name basis".

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>