Fix a few range checks which aren't working right because

	if (int < sizeof(...))

does the wrong thing if `int' is negative, due to `sizeof' returning unsigned.

In addition to comparisons, the patch makes CDROMVOL* ioctl more robust.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>