Btrfs: Simplify makefile

Single-colons will do here.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/Makefile b/fs/btrfs/Makefile
index 058a2da..6341cf7 100644
--- a/fs/btrfs/Makefile
+++ b/fs/btrfs/Makefile
@@ -16,10 +16,11 @@
 # Normal Makefile
 
 KERNELDIR := /lib/modules/`uname -r`/build
-all::
+all:
 	$(MAKE) -C $(KERNELDIR) M=`pwd` modules
-modules_install::
+modules_install:
 	$(MAKE) -C $(KERNELDIR) M=`pwd` modules_install
-clean::
+clean:
 	$(MAKE) -C $(KERNELDIR) M=`pwd` clean
+
 endif