Don't use an enum for a value read directly from the bitstream

The enum only defined values 1-7, while the variable can be set
to any value between 0 and 15 that is read from the bitstream
by FDKreadBits(hBs, 4).

This fixes undefined behaviour sanitizer errors.

Fixes: 19500/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_LIBFDK_AAC_fuzzer-5730449188192256

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg

libDRCdec/src/drcDec_reader.cpp

@@ -911,7 +911,7 @@ static void _skipEqCoefficients(HANDLE_FDK_BITSTREAM hBs) {
       firFilterOrder;
   int uniqueEqSubbandGainsCount, eqSubbandGainRepresentation,
       eqSubbandGainCount;
-  EQ_SUBBAND_GAIN_FORMAT eqSubbandGainFormat;
+  int eqSubbandGainFormat;
 
   eqDelayMaxPresent = FDKreadBits(hBs, 1);
   if (eqDelayMaxPresent) {
@@ -952,7 +952,7 @@ static void _skipEqCoefficients(HANDLE_FDK_BITSTREAM hBs) {
   uniqueEqSubbandGainsCount = FDKreadBits(hBs, 6);
   if (uniqueEqSubbandGainsCount > 0) {
     eqSubbandGainRepresentation = FDKreadBits(hBs, 1);
-    eqSubbandGainFormat = (EQ_SUBBAND_GAIN_FORMAT)FDKreadBits(hBs, 4);
+    eqSubbandGainFormat = FDKreadBits(hBs, 4);
     switch (eqSubbandGainFormat) {
       case GF_QMF32:
         eqSubbandGainCount = 32;