drivers: ethernet: Fix adin2111 multiple compatibles support

The adin2111 ethernet driver supports both adi,adin2111 and adi,adin1110
devicetree compatibles, however it failed to build when both compatibles
existed in the same devicetree. This may be an unusual configuration for
real systems, but was found when extending
tests/drivers/build_all/ethernet to cover both compatibles.

Signed-off-by: Maureen Helm <maureen.helm@analog.com>