malloc debug: fix LogFreeError error log

When free_track option is enabled and malloc debug detects error in
VerifyFreedPointer flow, if freed pointer's usable_size is more than
g_debug->config().fill_on_free_bytes(), the error log is not correct.

The max. bytes printed to error message should be the max bytes to
cmp, not usable size.

Bug: 124420174
Test: build pass and test pass
Change-Id: I41f35ab3330e49e0a6ad276d405bf4f6c3f0ea92