Clear static variables in X509 parser on error

In mbedtls_x509_parser.c there are some static arrays that are filled
during the integrity check and then read whenever an authentication
parameter is requested. However, they aren't cleared in case of an
integrity check failure, which can be problematic from a security
point of view. This patch clears these arrays in the case of failure.

Change-Id: I9d48f5bc71fa13e5a75d6c45b5e34796ef13aaa2
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>