jbd2: export __jbd2_debug for modular builds

The commit "jbd2: use a single printk for jbd_debug()" introduced a new function, __jbd2_debug. However it needs to be exported or the final modpost stage of the build will fail with:

ERROR: "__jbd2_debug" [fs/ext4/ext4.ko] undefined! make[1]: *** [__modpost] Error 1
make: *** [modules] Error 2

---

[Feel free to squash this into the original commit since it is in your dev branch.]

 fs/jbd2/journal.c | 1 +
 1 file changed, 1 insertion(+)

index 331fd59..4c8b8d4 100644
@@ -118,6 +118,7 @@ void __jbd2_debug(int level, const char *file, const char *func,
 	printk(KERN_DEBUG "%s: (%s, %u): %pV\n", file, func, line, &vaf);
 	va_end(args);
 }
+EXPORT_SYMBOL(__jbd2_debug);
 #endif
 
 /* Checksumming functions */

1.8.1.2

Thanks, I've merged this into the original commit and pushed out an updated dev branch.

- Ted