fbdev: uvesafb: remove DRIVER_ATTR() usage

It's better to be explicit and use the DRIVER_ATTR_RW() macro when
defining a driver's sysfs file.  Bonus is this fixes up a checkpatch.pl
warning.

This is part of a series to drop DRIVER_ATTR() from the tree entirely.

Acked-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>