ipmi: Fix kernel panic at ipmi_ssif_thread()

msg_written_handler() may set ssif_info->multi_data to NULL
when using ipmitool to write fru.

Before setting ssif_info->multi_data to NULL, add new local
pointer "data_to_send" and store correct i2c data pointer to
it to fix NULL pointer kernel panic and incorrect ssif_info->multi_pos.

Signed-off-by: Joeseph Chang <joechang@codeaurora.org>
Signed-off-by: Corey Minyard <cminyard@mvista.com>
Cc: stable@vger.kernel.org # 3.19-

drivers/char/ipmi/ipmi_ssif.c

@@ -891,6 +891,7 @@ static void msg_written_handler(struct ssif_info *ssif_info, int result,
 		 * for details on the intricacies of this.
 		 */
 		int left;
+		unsigned char *data_to_send;
 
 		ssif_inc_stat(ssif_info, sent_messages_parts);
 
@@ -899,6 +900,7 @@ static void msg_written_handler(struct ssif_info *ssif_info, int result,
 			left = 32;
 		/* Length byte. */
 		ssif_info->multi_data[ssif_info->multi_pos] = left;
+		data_to_send = ssif_info->multi_data + ssif_info->multi_pos;
 		ssif_info->multi_pos += left;
 		if (left < 32)
 			/*
@@ -912,7 +914,7 @@ static void msg_written_handler(struct ssif_info *ssif_info, int result,
 		rv = ssif_i2c_send(ssif_info, msg_written_handler,
 				  I2C_SMBUS_WRITE,
 				  SSIF_IPMI_MULTI_PART_REQUEST_MIDDLE,
-				  ssif_info->multi_data + ssif_info->multi_pos,
+				  data_to_send,
 				  I2C_SMBUS_BLOCK_DATA);
 		if (rv < 0) {
 			/* request failed, just return the error. */