HSD #14019448981: net: ethernet: altera: set correct pcs base address (#220)

commit d8f0fc5fed1be80e61eeef834454866777a66cc4 from
https://github.com/altera-opensource/linux-socfpga.git

 socfpga-6.1.55-lts.

pcs base address is not set correctly, this causes
pcs configuration failure. This patch is to cast the
pcs base address so that it can be offset correctly.

Signed-off-by: Swee Leong Ching <leong.ching.swee@intel.com>
Signed-off-by: Liwei Song <liwei.song@windriver.com>