Now umd0: size is in sectors, not bytes

So we have to check based on that correctly.  Darn it, bc7bc87941e7accb2ea8432b313f90fb6f934669 was incomplete.

Fixes [a hang in FF2] (http://forums.ppsspp.org/showthread.php?tid=1322&pid=69883#pid69883).

-[Unknown]