MdeModulePkg: Fix coding style issues

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1479

Fix issues that reported by Edk2 coding style check tool(ECC) that:
Comment description should end with period '.'

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Jian J Wang <jian.j.wang@intel.com>
Cc: Hao Wu <hao.a.wu@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Dandan Bi <dandan.bi@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

MdeModulePkg/Universal/FaultTolerantWriteDxe/FaultTolerantWriteSmmCommon.h

@@ -78,7 +78,7 @@ typedef struct {
 } SMM_FTW_GET_LAST_WRITE_HEADER;
 
 /**
-  Shared entry point of the module
+  Shared entry point of the module.
 
   @retval EFI_SUCCESS           The initialization finished successfully.
   @retval EFI_OUT_OF_RESOURCES  Allocate memory error
@@ -109,7 +109,7 @@ FtwSmmIsBufferOutsideSmmValid (
   );
 
 /**
-  Notify the system that the SMM FTW driver is ready
+  Notify the system that the SMM FTW driver is ready.
 **/
 VOID
 FtwNotifySmmReady (