DLM must depend on SYSFS

CONFIG_DLM=y and CONFIG_SYSFS=n results in the following compile error:

<-- snip -->

...
LD vmlinux
drivers/built-in.o:(.data+0x271e80): undefined reference to `kernel_subsys'
make: *** [vmlinux] Error 1

<-- snip -->

@@ -3,6 +3,7 @@
 
 config DLM
 	tristate "Distributed Lock Manager (DLM)"
+	depends on SYSFS
 	select IP_SCTP
 	help
 	A general purpose distributed lock manager for kernel or userspace