sysfs allocates PAGE_SIZE.  It is used by each R/W operation method.  Use
it instead of another buffer size.
Signed-off-by: NMilo(Woogyom) Kim <milo.kim@ti.com>
Acked-by: NJingoo Han <jg1.han@samsung.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>