make_cert: return error when invalid options are used
make_cert: return error when invalid options are used

Print_help was used in different contexts and returning no
error in that function was hiding the error when incorrect
options were used.

Change-Id: Ic3f71748be7ff8440c9d54810b986e9f177f4439
Signed-off-by: Roberto Vargas <d75e640c49defb97bd074f828210df57ed181e1f@arm.com>

achingupta/arm-trusted-firmware,achingupta/arm-trusted-firmware