MdeModulePkg: Use CopyMem instead of GUID assignment

MdeModulePkg: Use CopyMem instead of GUID assignment

GCC translates a simple assignment to memcpy, which EDKII doesn't provide.
See: https://www.mail-archive.com/edk2-devel@lists.01.org/msg11928.html

REF:https://bugzilla.tianocore.org/show_bug.cgi?id=2547

Signed-off-by: Daniel Schaefer <daniel.schaefer@hpe.com>
Cc: Abner Chang <abner.chang@hpe.com>
Cc: Gilbert Chen <gilbert.chen@hpe.com>
Cc: Leif Lindholm <leif@nuviainc.com>
Cc: Dandan Bi <dandan.bi@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Reviewed-by: Dandan Bi <dandan.bi@intel.com>