fix sbyte fails build

Author: kazu-321

src/ros2cs/rosidl_generator_cs/rosidl_generator_cs/generate_cs_impl.py

@@ -108,12 +108,12 @@ def get_marshal_type(type_):
     'float': 'float',
     'double': 'double',
     'long double': 'double',
-    'char': 'char',
-    'wchar': 'short',
+    'char': 'byte',
+    'wchar': 'char',
     'boolean': 'byte',
     'octet': 'byte',
     'uint8': 'byte',
-    'int8': 'char',
+    'int8': 'byte',
     'uint16': 'short',
     'int16': 'short',
     'uint32': 'int',
@@ -135,8 +135,8 @@ def get_marshal_array_type(type_):
     'float' : 'float',
     'double' : 'double',
     'long double': 'double',
-    'char' : 'char',
-    'wchar' : 'ushort',
+    'char' : 'byte',
+    'wchar' : 'char',
     'boolean' : 'bool',
     'octet' : 'byte',
     'uint8' : 'byte',