net: ag71xx: Use GFP_KERNEL instead of GFP_ATOMIC in 'ag71xx_rings_init()'

There is no need to use GFP_ATOMIC here, GFP_KERNEL should be enough.
The 'kcalloc()' just a few lines above, already uses GFP_KERNEL.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>