Fix error.c test suite relying on old name

tests/suites/test_suite_error.function

diff --git a/tests/suites/test_suite_error.function b/tests/suites/test_suite_error.function
index 4129f3d..a514cee 100644
--- a/tests/suites/test_suite_error.function
+++ b/tests/suites/test_suite_error.function
@@ -12,7 +12,7 @@
 {
     char buf[500];
 
-    error_strerror( code, buf, 500 );
+    polarssl_strerror( code, buf, 500 );
 
     TEST_ASSERT( strcmp( buf, result_str ) == 0 );
 }