ea4d2d0535
Currently, we create an immutable `GuestPtr` from `self` and call `as_raw` on it which correctly returns `*const u8`. However, since we're dealing with `GuestPtrMut` I thought it might make more sense to return `*mut u8` directly instead. This will be needed (and will save us from silly casts `*const _ as *mut _`) in plugging in `Iovec<'_>` into `std::io::IoSliceMut` in `fd_read` and `fd_pread` calls.