i40e: clamp debugfs nvm read command

This issue was identified by the coverity checker where we were
not checking the upper limit on reads, reported by Hannes
Frederic Sowa.

Implement more specific limits on reads (min 1k, max 4k)

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
CC: Hannes Frederic Sowa <hannes@stressinduktion.org>
Tested-by: Kavindya Deegala <kavindya.s.deegala@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>