net: ibm: emac: mal: add dcr_unmap to _remove

It's done in probe so it should be undone here.

Fixes: 1d3bb996481e ("Device tree aware EMAC driver")
Signed-off-by: Rosen Penev <rosenp@gmail.com>
Reviewed-by: Breno Leitao <leitao@debian.org>
Link: https://patch.msgid.link/20241008233050.9422-1-rosenp@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>