Minimal-printf: Fix wrapping of vsnprintf for ARM compiler

Substituting vsnprintf instead of __2vsnprintf allows calls to vsnprintf
to be substituted with the minimal-printf variant for the ARM toolchain.

Author: hugueskamba

platform/source/minimal-printf/mbed_printf_armlink_overrides.c

@@ -76,7 +76,7 @@ int $Sub$$__2vprintf(char *buffer, const char *format, ...)
     return result;
 }
 
-int $Sub$$__2vsnprintf(char *buffer, size_t length, const char *format, va_list arguments)
+int $Sub$$vsnprintf(char *buffer, size_t length, const char *format, va_list arguments)
 {
     return mbed_minimal_formatted_string(buffer, length, format, arguments, NULL);
 }