ethernet: ucc_geth: use UCC_GETH_{RX,TX}_BD_RING_ALIGNMENT macros directly

These macros both have the value 32, there's no point first
initializing align to a lower value.

If anything, one could throw in a
BUILD_BUG_ON(UCC_GETH_TX_BD_RING_ALIGNMENT < 4), but it's not worth it
- lots of code depends on named constants having sensible values.

Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>