Fix custom fwd and bwd for older PyTorch versions (#608)

#596 (comment)

mamba_ssm/utils/torch.py

@@ -1,16 +1,18 @@
 import torch
 from functools import partial
+from typing import Callable
 
-
-def custom_amp_decorator(dec, cuda_amp_deprecated):
-    def decorator(func):
-        return dec(func) if not cuda_amp_deprecated else partial(dec, func, device_type="cuda")
+def custom_amp_decorator(dec: Callable, cuda_amp_deprecated: bool):
+    def decorator(*args, **kwargs):
+        if cuda_amp_deprecated:
+            kwargs["device_type"] = "cuda"
+        return dec(*args, **kwargs)
     return decorator
 
 
-if hasattr(torch.amp, "custom_fwd"):
+if hasattr(torch.amp, "custom_fwd"): # type: ignore[attr-defined]
     deprecated = True
-    from torch.amp import custom_fwd, custom_bwd
+    from torch.amp import custom_fwd, custom_bwd # type: ignore[attr-defined]
 else:
     deprecated = False
     from torch.cuda.amp import custom_fwd, custom_bwd