net: stmicro: fix LS field mask in EEE configuration

This patch fixes the LS mask when setting EEE timer.
LS field is 10 bits long and not 11 as currently.

Signed-off-by: Joao Pinto <jpinto@synopsys.com>
Reported-By: Rayagond Kokatanur <rayagond@vayavyalabs.com>
Signed-off-by: David S. Miller <davem@davemloft.net>