Revert "net: macb: Fixed reading MII_LPA register"

This reverts commit 1b0c9914.

Commit 1b0c9914 ("net: macb: Fixed reading MII_LPA register")
causes 100Mbps does not work any more with SiFive FU540 GEM on the
HiFive Unleashed board. Revert it.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>