net: ethernet: ucc_geth: fix MEM_PART_MURAM mode

commit 8b8642af15ed14b9a7a34d3401afbcc274533e13 upstream.

Since commit 5093bb965a163 ("powerpc/QE: switch to the cpm_muram
implementation"), muram area is not part of immrbar mapping anymore
so immrbar_virt_to_phys() is not usable anymore.

Fixes: 5093bb965a163 ("powerpc/QE: switch to the cpm_muram implementation")
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Acked-by: David S. Miller <davem@davemloft.net>
Acked-by: Li Yang <pku.leo@gmail.com>
Signed-off-by: Scott Wood <oss@buserror.net>
[bwh: Backported to 3.2: adjust filename]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>