file-posix: Don't leak fd in hdev_get_max_segments

This fixes a leaked fd introduced in commit 9103f1ce.

Signed-off-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/file-posix.c

@@ -703,6 +703,9 @@ static int hdev_get_max_segments(const struct stat *st)
     }
 
 out:
+    if (fd != -1) {
+        close(fd);
+    }
     g_free(sysfspath);
     return ret;
 #else