MdeModulePkg Variable: Fix comment typo 'end' to 'start'

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1214
This patch only updates comment and function description, so has
no functionality impact.

This patch fixes comment typo 'end' to 'start' in GetStartPointer.

GetStartPointer for PEI and DXE has aligned function description,
but GetEndPointer does not.
This patch also aligns GetEndPointer's function description for
PEI and DXE.

Cc: Liming Gao <liming.gao@intel.com>
Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Jian J Wang <jian.j.wang@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>

MdeModulePkg/Universal/Variable/Pei/Variable.c

@@ -57,7 +57,7 @@ PeimInitializeVariableServices (
 
   @param VarStoreHeader  Pointer to the Variable Store Header.
 
-  @return Pointer to the first variable header
+  @return Pointer to the first variable header.
 
 **/
 VARIABLE_HEADER *
@@ -66,18 +66,22 @@ GetStartPointer (
   )
 {
   //
-  // The end of variable store
+  // The start of variable store
   //
   return (VARIABLE_HEADER *) HEADER_ALIGN (VarStoreHeader + 1);
 }
 
 
 /**
-  This code gets the pointer to the last variable memory pointer byte.
 
-  @param  VarStoreHeader  Pointer to the Variable Store Header.
+  Gets the pointer to the end of the variable storage area.
 
-  @return VARIABLE_HEADER* pointer to last unavailable Variable Header.
+  This function gets pointer to the end of the variable storage
+  area, according to the input variable store header.
+
+  @param VarStoreHeader  Pointer to the Variable Store Header.
+
+  @return Pointer to the end of the variable storage area.
 
 **/
 VARIABLE_HEADER *

MdeModulePkg/Universal/Variable/RuntimeDxe/Variable.c

@@ -681,7 +681,7 @@ GetStartPointer (
   )
 {
   //
-  // The end of variable store.
+  // The start of variable store.
   //
   return (VARIABLE_HEADER *) HEADER_ALIGN (VarStoreHeader + 1);
 }