MdeModulePkg/PiSmmCore: make type punning consistent

MdeModulePkg/PiSmmCore: make type punning consistent

The SmiHandlerRegister() function explicitly casts "SmiHandler" (of type
(SMI_HANDLER*)) to EFI_HANDLE, when outputting "DispatchHandle".

Apply the same cast in the counterpart function SmiHandlerUnRegister(),
which compares multiple "SmiHandler"s against the input "DispatchHandle".

This is a semantic cleanup; there is no functional change.

Cc: Eric Dong <eric.dong@intel.com>
Cc: Hao A Wu <hao.a.wu@intel.com>
Cc: Jian J Wang <jian.j.wang@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Eric Dong <eric.dong@intel.com>
Reviewed-by: Hao A Wu <hao.a.wu@intel.com>