eth/gasprice: fix eth_feeHistory blobGasRatio (#31246)

This change divides BlobGasUsed by MaxBlobGasPerBlock instead of
MaxBlobsPerBlock. Dividing by MaxBlobsPerBlock
meant the blobGasUsedRatio was an incorrect large number. This bug was
introduced by a typo
[here](ethereum/go-ethereum@e6f3ce7#diff-3357b2399699d7cf954c543cbfb02ff442eb24491e55f5e813e3cc85829b3e8dR110)

Fixes ethereum/go-ethereum#31245

eth/gasprice/feehistory.go

@@ -107,8 +107,8 @@ func (oracle *Oracle) processBlock(bf *blockFees, percentiles []float64) {
 	// Compute gas used ratio for normal and blob gas.
 	bf.results.gasUsedRatio = float64(bf.header.GasUsed) / float64(bf.header.GasLimit)
 	if blobGasUsed := bf.header.BlobGasUsed; blobGasUsed != nil {
-		maxBlobs := eip4844.MaxBlobsPerBlock(config, bf.header.Time)
-		bf.results.blobGasUsedRatio = float64(*blobGasUsed) / float64(maxBlobs)
+		maxBlobGas := eip4844.MaxBlobGasPerBlock(config, bf.header.Time)
+		bf.results.blobGasUsedRatio = float64(*blobGasUsed) / float64(maxBlobGas)
 	}
 
 	if len(percentiles) == 0 {