iwlwifi: pcie: avoid potential PNVM leaks

If we erroneously try to set the PNVM data again after it has
already been set, we could leak the old DMA memory. Avoid that
and warn, we shouldn't be doing this.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Fixes: 69725928 ("iwlwifi: read and parse PNVM file")
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/iwlwifi.20210115130252.929c2d680429.I086b9490e6c005f3bcaa881b617e9f61908160f3@changeid