qtnfmac: fix debugfs support for multiple cards

Fix merge artifact for commit 0b68fe10 ("qtnfmac: modify debugfs
to support multiple cards") and finally add debugfs support
for multiple qtnfmac wireless cards.

Signed-off-by: Sergey Matyukevich <sergey.matyukevich.os@quantenna.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>