Fix the regex

Author: mukhoakash

src/azure-cli/azure/cli/command_modules/acs/azurecontainerstorage/_helpers.py

@@ -414,7 +414,7 @@ def get_desired_resource_value_args(
 # Returns -1 if there is a problem with parsing the vm_size.
 def get_cores_from_sku(vm_size):
     cpu_value = -1
-    pattern = r'(\d+)([a-z])*(?=_v(\d+)[^_]*$|$)'
+    pattern = r'([a-z])+(\d+)[a-z]*(?=_v(\d+)[^_]*$|$)'
     match = re.search(pattern, vm_size.lower())
     if match:
         series_prefix = match.group(1)