zram: use DEVICE_ATTR_[RW|RO|WO] to define zram sys device attribute

zram: use DEVICE_ATTR_[RW|RO|WO] to define zram sys device attribute

In current zram, we use DEVICE_ATTR() to define sys device attributes.
SO, we need to set (S_IRUGO | S_IWUSR) permission and other arguments
manually.  Linux already provids the macro DEVICE_ATTR_[RW|RO|WO] to
define sys device attribute.  It is simple and readable.

This patch uses kernel defined macro DEVICE_ATTR_[RW|RO|WO] to define
zram device attribute.

Signed-off-by: Ganesh Mahendran <[email protected]>
Acked-by: Jerome Marchand <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: Nitin Gupta <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>