ps3vram: Use proc_create_data() instead of proc_create()

Use proc_create_data() to avoid race conditions.

Reported-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>
Cc: Jim Paris <jim@jtan.com>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>