e1000e: minor correction to name of bit in CTRL_EXT register

Bit 7 in the CTRL_REG register is actually the Software Definable Pin 3,
not the Software Definable Pin 7.

Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>