ionic: check cmd_regs before copying in or out

Since we now have potential cases of NULL cmd_regs and info_regs
during a reset recovery, and left NULL if a reset recovery has
failed, we need to check that they exist before we use them.
Most of the cases were covered in the original patch where we
verify before doing the ioreadb() for health or cmd status.
However, we need to protect a few uses of io mem that could
be hit in error recovery or asynchronous threads calls as well
(e.g. ethtool or devlink handlers).

Fixes: 219e1832 ("ionic: no fw read when PCI reset failed")
Reviewed-by: Brett Creeley <brett.creeley@amd.com>
Signed-off-by: Shannon Nelson <shannon.nelson@amd.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>