NetworkPkg/HttpDxe: use error handler epilogue in TlsConfigCertificate()

NetworkPkg/HttpDxe: use error handler epilogue in TlsConfigCertificate()

Introduce a FreeCACert label near the end of the function, so that we can
keep the FreePool(CACert) statement centralized for error and success
exits.

Cc: Jiaxin Wu <jiaxin.wu@intel.com>
Cc: Siyuan Fu <siyuan.fu@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Fu Siyuan <siyuan.fu@intel.com>
Reviewed-by: Jiaxin Wu <jiaxin.wu@intel.com>