wifi: libertas: handle possible spu_write_u16() errors

Check and handle (well, report at least, as it's done through the rest
of the module) possible 'spu_write_u16()' errors in 'if_spi_e2h()'.

Found by Linux Verification Center (linuxtesting.org) with SVACE.
Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230725060531.72968-5-dmantipov@yandex.ru

drivers/net/wireless/marvell/libertas/if_spi.c

@@ -826,11 +826,16 @@ static void if_spi_e2h(struct if_spi_card *card)
 		goto out;
 
 	/* re-enable the card event interrupt */
-	spu_write_u16(card, IF_SPI_HOST_INT_STATUS_REG,
+	err = spu_write_u16(card, IF_SPI_HOST_INT_STATUS_REG,
 			    ~IF_SPI_HICU_CARD_EVENT);
+	if (err)
+		goto out;
 
 	/* generate a card interrupt */
-	spu_write_u16(card, IF_SPI_CARD_INT_CAUSE_REG, IF_SPI_CIC_HOST_EVENT);
+	err = spu_write_u16(card, IF_SPI_CARD_INT_CAUSE_REG,
+			    IF_SPI_CIC_HOST_EVENT);
+	if (err)
+		goto out;
 
 	lbs_queue_event(priv, cause & 0xff);
 out: