i40e: Fix possible memory leak in i40e_dbg_dump_desc

I didn't notice that return in the code, fix it by
adding a goto out instead to free the memory.

Fixes:

> New smatch warnings:
> drivers/net/ethernet/intel/i40e/i40e_debugfs.c:832 i40e_dbg_dump_desc() warn: possible memory leak of 'ring'

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Joe Perches <joe@perches.com>
Tested-by: Jim Young <james.m.young@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>