Changed off_t to loff_t

- off_t is long, loff_t is long long (32bit vs. 64bit)
- exfat requites 64 bit to support larger than 2GB fs

Change-Id: I71e856cc6fa23dda254cc60fe1ecab2ce8608b8e

Conflicts:
	libexfat/mount.c
	libexfat/node.c