Free context in at the end of aes_crypt_xts_size()

in file tests/suite/test_suite_aes.function, aes_crypt_xts_size()
did not free the context upon the function exit.
The function now frees the context on exit.

Fixes #4176

Signed-off-by: JoeSubbiani <Joe.Subbiani@arm.com>
diff --git a/tests/suites/test_suite_aes.function b/tests/suites/test_suite_aes.function
index 754a167..a90277d 100644
--- a/tests/suites/test_suite_aes.function
+++ b/tests/suites/test_suite_aes.function
@@ -210,6 +210,8 @@
     /* Valid pointers are passed for builds with MBEDTLS_CHECK_PARAMS, as
      * otherwise we wouldn't get to the size check we're interested in. */
     TEST_ASSERT( mbedtls_aes_crypt_xts( &ctx, MBEDTLS_AES_ENCRYPT, length, data_unit, src, output ) == retval );
+exit:
+    mbedtls_aes_xts_free( &ctx );
 }
 /* END_CASE */