MIPS: Fix MacroAssembler::AssertFunction()

MIPS: Fix MacroAssembler::AssertFunction()

Porting mistake in ccbb4ff0 '[builtins] Unify the various versions of [[Call]]
with a Call builtin.', which only showed as debug assertion in later commit
db2ba190 '[runtime] Replace many buggy uses of %_CallFunction with %_Call.'

Use temporary register rather than push/pop of 'object' register.

BUG=
TEST=cctest/test-api/SetFunctionEntryHook, cctest/test-serialize/PerIsolateSnapshotBlobs, ...

Review URL: https://codereview.chromium.org/1309163006

Cr-Commit-Position: refs/heads/master@{#30643}