nfp: don't set aux pointers if ioremap failed

If ioremap of PCIe ctrl memory failed we can still get to it through
PCI config space, therefore we allow ioremap() to fail.  When if fails,
however, we must leave all the IOMEM pointers as NULL.  Currently we
would calculate csr and em pointers, adding offsets to the potential
NULL value and therefore making the NULL-checks throughout the code
ineffective.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>