CryptoPkg: Update OPTIONAL location for BaseCryptLibMbedTls

REF:https://bugzilla.tianocore.org/show_bug.cgi?id=4740

There is a wrong usage for OPTIONAL.

Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Yi Li <yi1.li@intel.com>
Signed-off-by: Wenxing Hou <wenxing.hou@intel.com>
Reviewed-by: Yi Li <yi1.li@intel.com>
2 files changed