kernel: Correct class/struct mixups.

Almost certainly harmless. Spotted by Clang.

headers/private/kernel/vm/VMArea.h

@@ -148,9 +148,9 @@ protected:
 			status_t			Init(const char* name, uint32 allocationFlags);
 
 protected:
-			friend class VMAddressSpace;
+			friend struct VMAddressSpace;
-			friend class VMKernelAddressSpace;
+			friend struct VMKernelAddressSpace;
-			friend class VMUserAddressSpace;
+			friend struct VMUserAddressSpace;
 
 protected:
 			void				SetBase(addr_t base)	{ fBase = base; }

headers/private/kernel/vm/VMCache.h

@@ -20,7 +20,7 @@
 
 
 struct kernel_args;
-class ObjectCache;
+struct ObjectCache;
 
 
 enum {

src/system/kernel/device_manager/IORequest.h

@@ -25,7 +25,7 @@
 										   allocations won't fail */
 #define B_DELETE_IO_REQUEST		0x04	/* delete request when finished */
 
-struct DMABuffer;
+class DMABuffer;
 struct IOOperation;
 
 typedef struct IOOperation io_operation;
@@ -85,8 +85,8 @@ private:
 };
 
 
-class IORequest;
+struct IORequest;
-class IORequestOwner;
+struct IORequestOwner;
 
 
 class IORequestChunk {

src/system/kernel/scheduler/scheduler_common.h

@@ -31,8 +31,8 @@
 namespace Scheduler {
 
 
-struct CPUEntry;
+class CPUEntry;
-struct CoreEntry;
+class CoreEntry;
 
 const int kLowLoad = kMaxLoad * 20 / 100;
 const int kTargetLoad = kMaxLoad * 55 / 100;

src/system/kernel/slab/HashedObjectCache.h

@@ -93,7 +93,7 @@ private:
 			typedef BOpenHashTable<Definition, false, false,
 				InternalAllocator> HashTable;
 
-			friend class Definition;
+			friend struct Definition;
 
 private:
 			void				_ResizeHashTableIfNeeded(uint32 flags);

src/system/kernel/slab/MemoryManager.h

@@ -94,7 +94,7 @@ private:
 				Area*			GetArea() const;
 			};
 
-			friend class MetaChunk;
+			friend struct MetaChunk;
 			typedef DoublyLinkedList<MetaChunk> MetaChunkList;
 
 			struct Area : DoublyLinkedListLinkImpl<Area> {

src/system/kernel/slab/ObjectCache.h

@@ -18,7 +18,6 @@
 #include "slab_debug.h"
 
 
-class AllocationTrackingInfo;
 struct ResizeRequest;