python: Fix deprecated decorator

The deprecation message was firing during the decoration process instead of firing upon first call to deprecated function. The message now fires only if the deprected function is called.

Change-Id: I2d510eb24884fdba0123e71e8472db68ae9d2ce4
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/67334
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Richard Cooper <richard.cooper@arm.com>

src/python/m5/util/__init__.py

@@ -108,8 +108,12 @@ def deprecated(replacement=None, logger=warn):
                     message += f" Prefer {replacement} instead."
             logger(message)
 
-        notifyDeprecation()
-        return func
+        @wraps(func)
+        def wrapper(*args, **kwargs):
+            notifyDeprecation()
+            return func(*args, **kwargs)
+
+        return wrapper
 
     return decorator