Fix AssemblerMIPS64Test.LongBalc() running out of memory.

Pre-allocate the necessary buffer because the reallocation
strategy doesn't work well for a test of this size.

Test: m test-art-host-gtest-assembler_mips64_test
Change-Id: I16bc75f0ae83a62e5f3ed2cd8228dd40f0eb9524
1 file changed