kernel/shared_memory: Add a const qualified member function overload for GetPointer()

Given this doesn't mutate instance state, we can provide a
const-qualified variant as well.

src/core/hle/kernel/shared_memory.cpp

@@ -136,4 +136,8 @@ u8* SharedMemory::GetPointer(std::size_t offset) {
     return backing_block->data() + backing_block_offset + offset;
 }
 
+const u8* SharedMemory::GetPointer(std::size_t offset) const {
+    return backing_block->data() + backing_block_offset + offset;
+}
+
 } // namespace Kernel

src/core/hle/kernel/shared_memory.h

@@ -113,10 +113,17 @@ public:
     /**
      * Gets a pointer to the shared memory block
      * @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
+     * @return A pointer to the shared memory block from the specified offset
      */
     u8* GetPointer(std::size_t offset = 0);
 
+    /**
+     * Gets a constant pointer to the shared memory block
+     * @param offset Offset from the start of the shared memory block to get pointer
+     * @return A constant pointer to the shared memory block from the specified offset
+     */
+    const u8* GetPointer(std::size_t offset = 0) const;
+
 private:
     explicit SharedMemory(KernelCore& kernel);
     ~SharedMemory() override;