IAR: Fix v850 assembler support file extensions

Fix the file extension added by commit 158f3795b8 (IAR: Add v850
assembler support, 2019-09-23, v3.16.0-rc1~70^2).

Issue: #17264

Modules/Compiler/IAR-ASM.cmake

@@ -40,7 +40,7 @@ elseif("${CMAKE_ASM${ASM_DIALECT}_COMPILER_ARCHITECTURE_ID}" STREQUAL "MSP430")
 elseif("${CMAKE_ASM${ASM_DIALECT}_COMPILER_ARCHITECTURE_ID}" STREQUAL "V850")
   set(CMAKE_ASM_COMPILE_OBJECT  "<CMAKE_ASM_COMPILER> -S <SOURCE> <DEFINES> <INCLUDES> <FLAGS> -o <OBJECT>")
   __compiler_iar_xlink(ASM)
-  set(CMAKE_ASM_SOURCE_FILE_EXTENSIONS r85;asm;msa)
+  set(CMAKE_ASM_SOURCE_FILE_EXTENSIONS s85;asm;msa)
 
 else()
   message(FATAL_ERROR "CMAKE_ASM${ASM_DIALECT}_COMPILER_ARCHITECTURE_ID not detected. This should be automatic.")