iwlwifi: pcie: handle pcim_iomap_table() failures better

iwlwifi: pcie: handle pcim_iomap_table() failures better

pcim_iomap_table() might return NULL, so we shouldn't unconditionally
dereference the return value by taking the [0] entry.

Handle this better by checking for NULL first, and then separately
checking if the [0] entry is NULL.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20210612142637.9aa4f0e3574a.I458b283f203d5f927f00be1bfbd4b8ebf11c5ae4@changeid
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>