ath79: update WA/XC devices UBNT_VERSION to 8.5.3

ath79: update WA/XC devices UBNT_VERSION to 8.5.3

Ubiquiti WA devices with newer hw version 2011K require UBNT_VERSION
to be at least 8.5.3, otherwise the image is rejected:

   New ver: WA.ar934x.v8.5.0-42.OpenWrt-r10947-65030d81f3
   Versions: New(525568) 8.5.0, Required(525571) 8.5.3
   Invalid version 'WA.ar934x.v8.5.0-42.OpenWrt-r10947-65030d81f3'

For consistency, also increase version number for XC devices.

Tested-by: Pedro <pedrowrt@cas.cat>
Signed-off-by: Roger Pueyo Centelles <roger.pueyo@guifi.net>