i40e: do not take NVM ownership for SR read

We do not need to acquire NVM for Shadow RAM XSUM calculation, as we only
read from SR through SRCTL register for which having the ownership is not
required.

Change-ID: Ie238a8f09917d1d25f24cc7cec271951ac7b98f2
Signed-off-by: Kamil Krawczyk <kamil.krawczyk@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>