i40e: Reduce stack in i40e_dbg_dump_desc

Reduce stack use by using kmemdup and not using a very
large struct on stack.

In function ‘i40e_dbg_dump_desc’:
warning: the frame size of 8192 bytes is larger than 2048 bytes [-Wframe-larger-than=]

Signed-off-by: Joe Perches <joe@perches.com>
Tested-by: Jim Young <jamesx.m.young@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>