[PATCH] uapi: fix linux/btrfs.h userspace compilation error

[Dmitry V. Levin]

Stop using NULL to fix the following linux/btrfs.h userspace compilation
error:

/usr/include/linux/btrfs.h: In function 'btrfs_err_str':
/usr/include/linux/btrfs.h:740:11: error: 'NULL' undeclared (first use in this function)
    return NULL;

Signed-off-by: Dmitry V. Levin <ldv@xxxxxxxxxxxx>
---
 include/uapi/linux/btrfs.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h
index db4c253..01c612f 100644
--- a/include/uapi/linux/btrfs.h
+++ b/include/uapi/linux/btrfs.h
@@ -737,7 +737,7 @@ static inline char *btrfs_err_str(enum btrfs_err_code err_code)
 			return "add/delete/balance/replace/resize operation "\
 				"in progress";
 		default:
-			return NULL;
+			return 0;
 	}
 }
 
-- 
ldv