[Hotfix] Avoid fused RMSnorm import error without apex (#5985)

Co-authored-by: Edenzzzz <wtan45@wisc.edu>

colossalai/shardformer/layer/normalization.py

@@ -42,7 +42,7 @@ try:
             return output
 
 except ImportError:
-    warnings.warn("Please install apex from source (https://github.com/NVIDIA/apex) to use the fused layernorm kernel")
+    warnings.warn("Please install apex from source (https://github.com/NVIDIA/apex) to use the fused RMSNorm kernel")
 
 FAST_LAYERNORM_SUPPORTED_SIZE = [
     1024,
@@ -270,12 +270,6 @@ class FusedRMSNorm(BaseLayerNorm):
         Returns:
             nn.Module: FusedRMSNorm module.
         """
-        try:
-            pass
-        except ImportError:
-            raise ImportError(
-                "Please install apex from source (https://github.com/NVIDIA/apex) to use the fused RMS normalization kernel"
-            )
 
         LazyInitContext.materialize(module)
 
@@ -284,11 +278,18 @@ class FusedRMSNorm(BaseLayerNorm):
         eps = module.variance_epsilon if hasattr(module, "variance_epsilon") else module.eps
         elementwise_affine = getattr(module, "elementwise_affine", True)
 
+        try:
             rmsnorm = FusedRMSNormWithHook(
                 normalized_shape=normalized_shape,
                 eps=eps,
                 elementwise_affine=elementwise_affine,
             )
+        except ImportError:
+            warnings.warn(
+                "Module replacement failed.\
+                Please install apex from source (https://github.com/NVIDIA/apex) to use the fused RMS normalization kernel"
+            )
+            return module
 
         rmsnorm.weight = module.weight