New MD API: rename functions from _ext to _ret

The _ext suffix suggests "new arguments", but the new functions have
the same arguments. Use _ret instead, to convey that the difference is
that the new functions return a value.
diff --git a/tests/suites/test_suite_mdx.function b/tests/suites/test_suite_mdx.function
index 387e7ee..648a9cc 100644
--- a/tests/suites/test_suite_mdx.function
+++ b/tests/suites/test_suite_mdx.function
@@ -19,7 +19,7 @@
 
     strncpy( (char *) src_str, text_src_string, sizeof(src_str) - 1 );
 
-    ret = mbedtls_md2_ext( src_str, strlen( (char *) src_str ), output );
+    ret = mbedtls_md2_ret( src_str, strlen( (char *) src_str ), output );
     TEST_ASSERT( ret == 0 ) ;
     hexify( hash_str, output, sizeof  output );
 
@@ -41,7 +41,7 @@
 
     strncpy( (char *) src_str, text_src_string, sizeof(src_str) - 1 );
 
-    ret = mbedtls_md4_ext( src_str, strlen( (char *) src_str ), output );
+    ret = mbedtls_md4_ret( src_str, strlen( (char *) src_str ), output );
     TEST_ASSERT( ret == 0 );
     hexify( hash_str, output, sizeof  output );
 
@@ -63,7 +63,7 @@
 
     strncpy( (char *) src_str, text_src_string, sizeof(src_str) - 1 );
 
-    ret = mbedtls_md5_ext( src_str, strlen( (char *) src_str ), output );
+    ret = mbedtls_md5_ret( src_str, strlen( (char *) src_str ), output );
     TEST_ASSERT( ret == 0 );
     hexify( hash_str, output, sizeof  output );
 
@@ -85,7 +85,7 @@
 
     strncpy( (char *) src_str, text_src_string, sizeof(src_str) - 1 );
 
-    ret = mbedtls_ripemd160_ext( src_str, strlen( (char *) src_str ), output );
+    ret = mbedtls_ripemd160_ret( src_str, strlen( (char *) src_str ), output );
     TEST_ASSERT( ret == 0 );
     hexify( hash_str, output, sizeof output );