nfc: nci: fix possible NULL pointer dereference in send_acknowledge()

Handle memory allocation failure from nci_skb_alloc() (calling
alloc_skb()) to avoid possible NULL pointer dereference.
Reported-by: 黄思聪 <huangsicong@iie.ac.cn>
Fixes: 391d8a2d ("NFC: Add NCI over SPI receive")
Cc: <stable@vger.kernel.org>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/20231013184129.18738-1-krzysztof.kozlowski@linaro.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/nfc/nci/spi.c

@@ -151,6 +151,8 @@ static int send_acknowledge(struct nci_spi *nspi, u8 acknowledge)
 	int ret;
 
 	skb = nci_skb_alloc(nspi->ndev, 0, GFP_KERNEL);
+	if (!skb)
+		return -ENOMEM;
 
 	/* add the NCI SPI header to the start of the buffer */
 	hdr = skb_push(skb, NCI_SPI_HDR_LEN);