ixgbe: fix variable set but not used warnings by gcc 4.6

Caught with gcc 4.6 -Wunused-but-set-variable

Remove unused napi_vectors variable.

Fix the use of reset_bit in ixgbe_reset_hw_X540()

Signed-off-by: Emil Tantilov <emil.s.tantilov@intel.com>
Tested-by: Stephen Ko <stephen.s.ko@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>