iwlwifi: fix fw/img.c license statement

We still had the entire license statement here, but with BSD,
so the SPDX tag was not matching the actual text. Fix that
and remove all the texts since they're no longer needed.

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.20211017123741.328c2b33081c.Ib3570e8f214538a878204cc2b0b612b5ed0571b3@changeid


Signed-off-by: Luca Coelho <luciano.coelho@intel.com>