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>