ixgbe: Add bounds check for x540 LED functions

This is an extension of commit 003287e0

 ("ixgbevf: Correct parameter
sent to LED function"); add bounds checking to x540 functions to ensure the
index is valid.

Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>