Correct type hint in functional.py (#992)

Author: sxndqc

bitsandbytes/functional.py

@@ -890,7 +890,7 @@ def quantize_fp4(A: Tensor, absmax: Tensor = None, out: Tensor = None, blocksize
 def quantize_nf4(A: Tensor, absmax: Tensor = None, out: Tensor = None, blocksize=64, compress_statistics=False, quant_storage=torch.uint8):
     return quantize_4bit(A, absmax, out, blocksize, compress_statistics, 'nf4', quant_storage)
 
-def quantize_4bit(A: Tensor, absmax: Tensor = None, out: Tensor = None, blocksize=64, compress_statistics=False, quant_type='fp4', quant_storage=torch.uint8) -> Tensor:
+def quantize_4bit(A: Tensor, absmax: Tensor = None, out: Tensor = None, blocksize=64, compress_statistics=False, quant_type='fp4', quant_storage=torch.uint8) -> (Tensor, QuantState):
     """
     Quantize tensor A in blocks of 4-bit values.