Fujitsu: Fix C90 standard flags

Fix typos from commit 3c867cff (Fujitsu: Add support for the Fujitsu
compiler in Trad mode, 2020-12-22).

Modules/Compiler/Fujitsu-C.cmake

@@ -4,9 +4,9 @@ include(Compiler/Fujitsu)
 __compiler_fujitsu(C)
 
 if(CMAKE_C_COMPILER_VERSION VERSION_GREATER_EQUAL 4)
-  set(CMAKE_C89_STANDARD_COMPILE_OPTION  -std=c89)
-  set(CMAKE_C89_EXTENSION_COMPILE_OPTION -std=gnu89)
-  set(CMAKE_C89_STANDARD__HAS_FULL_SUPPORT ON)
+  set(CMAKE_C90_STANDARD_COMPILE_OPTION  -std=c89)
+  set(CMAKE_C90_EXTENSION_COMPILE_OPTION -std=gnu89)
+  set(CMAKE_C90_STANDARD__HAS_FULL_SUPPORT ON)
 
   set(CMAKE_C99_STANDARD_COMPILE_OPTION  -std=c99)
   set(CMAKE_C99_EXTENSION_COMPILE_OPTION -std=gnu99)