Initialize ret from test code
Initialize ret from test code

The test function mbedtls_mpi_lt_mpi_ct did not initialize ret in test
code. If there was a bug in library code whereby the library function
mbedtls_mpi_lt_mpi_ct() did not set ret when it should, we might have
missed it if ret happened to contain the expected value. So initialize
ret to a value that we never expect.

Signed-off-by: Gilles Peskine <f805f64266d288fc5467baa7be6cd0ff366f477b@arm.com>

ARMmbed/mbedtls,NXPmicro/mbedtls,ARMmbed/mbedtls,NXPmicro/mbedtls,ARMmbed/mbedtls,NXPmicro/mbedtls,NXPmicro/mbedtls,Mbed-TLS/mbedtls,ARMmbed/mbedtls,Mbed-TLS/mbedtls,Mbed-TLS/mbedtls,Mbed-TLS/mbedtls