AK: Cast pointer in FixedMemoryStream::read_in_place(count)

I didn't notice this before because I only ever called it with u8. Oops!

AK/MemoryStream.h

@@ -64,7 +64,7 @@ public:
                 return Error::from_string_view_or_print_error_and_return_errno("Tried to obtain a non-const span from a read-only FixedMemoryStream"sv, EINVAL);
         }
 
-        Span<T> span { m_bytes.offset_pointer(m_offset), count };
+        Span<T> span { reinterpret_cast<T*>(m_bytes.offset_pointer(m_offset)), count };
         TRY(discard(sizeof(T) * count));
         return span;
     }