9p: fix put_data error handling

Abhishek Kulkarni pointed out an inconsistency in the way
errors are returned from p9_put_data.  On deeper exploration it
seems the error handling for this path was completely wrong.
This patch adds checks for allocation problems and propagates
errors correctly.
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>

net/9p/conv.c

@@ -451,8 +451,10 @@ p9_put_data(struct cbuf *bufp, const char *data, int count,
 		   unsigned char **pdata)
 {
 	*pdata = buf_alloc(bufp, count);
+	if (*pdata == NULL)
+		return -ENOMEM;
 	memmove(*pdata, data, count);
-	return count;
+	return 0;
 }
 
 static int
@@ -460,6 +462,8 @@ p9_put_user_data(struct cbuf *bufp, const char __user *data, int count,
 		   unsigned char **pdata)
 {
 	*pdata = buf_alloc(bufp, count);
+	if (*pdata == NULL)
+		return -ENOMEM;
 	return copy_from_user(*pdata, data, count);
 }