wifi: brcmfmac: Fix a typo "unknow"

It should be "unknown".
Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20221101170252.1032085-1-j.neuschaefer@gmx.net

drivers/net/wireless/broadcom/brcm80211/brcmfmac/sdio.c

@@ -1884,7 +1884,7 @@ static uint brcmf_sdio_readframes(struct brcmf_sdio *bus, uint maxframes)
 		}
 
 		rd->len_left = rd->len;
-		/* read header first for unknow frame length */
+		/* read header first for unknown frame length */
 		sdio_claim_host(bus->sdiodev->func1);
 		if (!rd->len) {
 			ret = brcmf_sdiod_recv_buf(bus->sdiodev,