e1000: sparse warnings fixes

Fix sparse warnings and problems from e1000 driver.

Added a sparse fix for the module param array index
-- Auke

Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: Auke Kok <auke-jan.h.kok@intel.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>