net: ethernet: cs89x0: remove stale CONFIG_MACH_MX31ADS reference
The legacy ARM board file for MACH_MX31ADS was removed in commit
c93197b0041d ("ARM: imx: Remove i.MX31 board files"), but a reference
to it remained in the cs89x0 driver. Drop this unused code.
Signed-off-by: Ethan Nelson-Moore <enelsonmoore@gmail.com>
Fixes: c93197b0041d ("ARM: imx: Remove i.MX31 board files")
Link: https://patch.msgid.link/20260509023732.42256-1-enelsonmoore@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>