CryptoPkg/BaseCryptLibOnProtocolPpi: Add missing comments

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=2552

DxeCryptLibConstructor have no comments for it, add comments for it.

Cc: Jian J Wang <jian.j.wang@intel.com>
Cc: Xiaoyu Lu <xiaoyux.lu@intel.com>
Signed-off-by: Guomin Jiang <guomin.jiang@intel.com>
Reviewed-by: Shenglei Zhang <shenglei.zhang@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
Reviewed-by: Xiaoyu Lu <xiaoyux.lu@intel.com>

CryptoPkg/Library/BaseCryptLibOnProtocolPpi/DxeCryptLib.c

@@ -32,6 +32,15 @@ GetCryptoServices (
   return (VOID *)mCryptoProtocol;
 }
 
+/**
+  Locate the valid Crypto Protocol.
+
+  @param  ImageHandle   The firmware allocated handle for the EFI image.
+  @param  SystemTable   A pointer to the EFI System Table.
+
+  @retval EFI_SUCCESS   The constructor executed correctly.
+  @retval EFI_NOT_FOUND Found no valid Crypto Protocol.
+**/
 EFI_STATUS
 EFIAPI
 DxeCryptLibConstructor (