bnxt_en: Check for zero dir entries in NVRAM.

If firmware goes into unstable state, HWRM_NVM_GET_DIR_INFO firmware
command may return zero dir entries. Return error in such case to
avoid zero length dma buffer request.

Fixes: c0c050c5 ("bnxt_en: New Broadcom ethernet driver.")
Signed-off-by: Vasundhara Volam <vasundhara-v.volam@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/broadcom/bnxt/bnxt_ethtool.c

@@ -2323,6 +2323,9 @@ static int bnxt_get_nvram_directory(struct net_device *dev, u32 len, u8 *data)
 	if (rc != 0)
 		return rc;
 
+	if (!dir_entries || !entry_length)
+		return -EIO;
+
 	/* Insert 2 bytes of directory info (count and size of entries) */
 	if (len < 2)
 		return -EINVAL;