mbedtls_test_read_mpi_core: allow odd number of hex digits

Test functions must now take a char* argument rather than data_t*. This does
not affect existing test data.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/tests/suites/test_suite_mpi.function b/tests/suites/test_suite_mpi.function
index d450197..2528b9c 100644
--- a/tests/suites/test_suite_mpi.function
+++ b/tests/suites/test_suite_mpi.function
@@ -728,7 +728,7 @@
 /* END_CASE */
 
 /* BEGIN_CASE */
-void mpi_core_lt_ct( data_t * input_X, data_t * input_Y, int exp_ret )
+void mpi_core_lt_ct( char *input_X, char *input_Y, int exp_ret )
 {
     mbedtls_mpi_uint *X = NULL;
     size_t X_limbs;