iwlwifi: queue: bail out on invalid freeing

[ Upstream commit 0bed6a2a

 ]

If we find an entry without an SKB, we currently continue, but
that will just result in an infinite loop since we won't increment
the read pointer, and will try the same thing over and over again.
Fix this.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/iwlwifi.20210122144849.abe2dedcc3ac.Ia6b03f9eeb617fd819e56dd5376f4bb8edc7b98a@changeid


Signed-off-by: Sasha Levin <sashal@kernel.org>