Change proc_dir_entry->size to be loff_t to represent files like
/proc/vmcore for 32bit systems with more than 4G memory.

Needed for seeing correct size for /proc/vmcore for 32-bit systems with >
4G RAM.
Signed-off-by: Maneesh Soni <maneesh@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>