net/i40e: fix null checks

net/i40e: fix null checks

This patch fixes the issues reported by Coverity of 'Dereference
before null check', by deleting unnecessary null checks, or moving
null checks to before the offending use of the pointer.

Coverity issue: 13298, 13299, 13294, 13301, 119267

Fixes: 8e109464c022 ("i40e: allow vector Rx and Tx usage")
Fixes: a778a1fa2e4e ("i40e: set up and initialize flow director")
Fixes: a778a1fa2e4e ("i40e: set up and initialize flow director")
Fixes: 4861cde46116 ("i40e: new poll mode driver")

Signed-off-by: Helin Zhang <helin.zhang@intel.com>
Acked-by: John McNamara <john.mcnamara@intel.com>