bcm47xx: Fix lzma-loader compilation

Fixes:
```
LzmaDecode.c: In function 'RangeDecoderReverseBitTreeDecode':
LzmaDecode.c:199:5: error: 'symbol' undeclared (first use in this function)
  199 |     symbol |= (bit << i);
      |     ^~~~~~
LzmaDecode.c:199:5: note: each undeclared identifier is reported only once for each function it appears in
```

Fixes: 4ffd5aa239c1 ("treewide: fix coccinelle checks")
Signed-off-by: Hauke Mehrtens <[email protected]>

target/linux/bcm47xx/image/lzma-loader/src/LzmaDecode.c

@@ -185,6 +185,7 @@ int RangeDecoderReverseBitTreeDecode(CProb *probs, int numLevels, CRangeDecoder
 {
   int mi = 1;
   int i;
+  int symbol = 0;
   #ifdef _LZMA_LOC_OPT
   RC_INIT_VAR
   #endif
@@ -202,7 +203,7 @@ int RangeDecoderReverseBitTreeDecode(CProb *probs, int numLevels, CRangeDecoder
   #ifdef _LZMA_LOC_OPT
   RC_FLUSH_VAR
   #endif
-  return 0;
+  return symbol;
 }
 
 Byte LzmaLiteralDecode(CProb *probs, CRangeDecoder *rd)