xhe-aac: Fix range issue with mp4bitmux

This CL prevent coef value from exceeding allowed range.

Bug: 449005879
Flag: android.media.codec.xhe_aac_encoder
Test: atest MctsMediaEncoderTestCases:EncoderTestXheAac
Test: atest MctsMediaEncoderTestCases:EncDecTestXheAac
Test: atest MctsMediaV2TestCases -- --module-arg MctsMediaV2TestCases:instrumentation-arg:codec-prefix:=c2.android.xheaac.encoder
Change-Id: I06071ab74dfc40bc1023ba2b733723bb2485d278