Rename mbedtls_error_add_ext to mbedtls_error_add

This function was previously called mbedtls_error_add_ext because there
was a macro called mbedtls_error_add. That later got capitalised which
allows the function to now be named mbedtls_error_add.

Signed-off-by: Chris Jones <christopher.jones@arm.com>
diff --git a/include/mbedtls/error.h b/include/mbedtls/error.h
index 52b8188..aabbe6c 100644
--- a/include/mbedtls/error.h
+++ b/include/mbedtls/error.h
@@ -122,11 +122,11 @@
 /**
  * \brief Combines a high-level and low-level error code together.
  *
- *        Wrapper macro for mbedtls_error_add_ext(). See that function for
+ *        Wrapper macro for mbedtls_error_add(). See that function for
  *        more details.
  */
 #define MBEDTLS_ERROR_ADD( high, low ) \
-        mbedtls_error_add_ext( high, low, __FILE__, __LINE__ )
+        mbedtls_error_add( high, low, __FILE__, __LINE__ )
 
 #if defined(MBEDTLS_TEST_HOOKS)
 /**
@@ -154,7 +154,7 @@
  * \param file      file where this error code addition occured.
  * \param line      line where this error code addition occured.
  */
-static inline int mbedtls_error_add_ext( int high, int low,
+static inline int mbedtls_error_add( int high, int low,
                                      const char *file, int line )
 {
 #if defined(MBEDTLS_TEST_HOOKS)