btrfs-progs: fix build of btrfs-show-super

The standalone utility btrfs-show-super has been obsoleted by 'btrfs
inspect-internal dump-super' but it's still in the repository and should
build in case somebody still uses it.

Reported-by: "John L. Center" <jlcenter15@gmail.com>
Signed-off-by: David Sterba <dsterba@suse.com>

btrfs-show-super.c

@@ -18,7 +18,7 @@
 
 #include "utils.h"
 #include "commands.h"
-#include "cmds-inspect-dump-super.h"
+#include "help.h"
 
 int main(int argc, char **argv)
 {