sh_eth: use EDMR_SRST_GETHER in sh_eth_check_reset()

sh_eth_check_reset() uses a bare number where EDMR_SRST_GETHER would fit,
i.e. the receive/trasmit software reset bits that comprise EDMR_SRST_GETHER
read as 1  while the corresponding reset is in progress and thus, when both
are 0, the reset is complete.

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: David S. Miller <davem@davemloft.net>