iwlwifi: mvm: don't restart HW if suspend fails with unified image

For unified images, we shouldn't restart the HW if suspend fails.  The
only reason for restarting the HW with non-unified images is to go
back to the D0 image.

Fixes: 23ae6128 ("iwlwifi: mvm: Do not switch to D3 image on suspend")
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>