kernel/shared_memory: Make GetPointer() take a std::size_t instead of a u32

Makes the interface nicer to use in terms of 64-bit code, as it makes it
less likely for one to get truncation warnings (and also makes sense in
the context of the rest of the interface where 64-bit types are used for
sizes and offsets

src/core/hle/kernel/shared_memory.cpp

@@ -132,7 +132,7 @@ VMAPermission SharedMemory::ConvertPermissions(MemoryPermission permission) {
     return static_cast<VMAPermission>(masked_permissions);
 }
 
-u8* SharedMemory::GetPointer(u32 offset) {
+u8* SharedMemory::GetPointer(std::size_t offset) {
     return backing_block->data() + backing_block_offset + offset;
 }
 

src/core/hle/kernel/shared_memory.h

@@ -115,7 +115,7 @@ public:
      * @param offset Offset from the start of the shared memory block to get pointer
      * @return Pointer to the shared memory block from the specified offset
      */
-    u8* GetPointer(u32 offset = 0);
+    u8* GetPointer(std::size_t offset = 0);
 
 private:
     explicit SharedMemory(KernelCore& kernel);