Clean up parameter names in ManagedRegisterEntrySpills.

Avoid the double underscore prefix. Identifiers starting
with two underscores are reserved for C++ implemenations,
i.e. the C++ compiler and the standard library.

Test: Rely on TreeHugger.
Change-Id: If6d80a63badb2f95f4cbcef946c10911c954419b
1 file changed