Linux 3.10 compat: replace PDE()->data with PDE_DATA().

torvalds/linux@d9dda78b

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>
Linux 3.10 compat: add missing include of linux/slab.h

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>