ixgbevf: Correct parameter sent to LED function

The second parameter of these functions is the index to the led we
are interested in affecting.  However we were mistakenly passing
the offset in the register.  This patch corrects that and adds some
bonds checking which would hopefully make bugs like this more noticeable
in the future.

Signed-off-by: Don Skidmore <donald.c.skidmore@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>