staging: zcache: include module.h for MODULE_LICENSE

The oncoming cleanup of module.h usage requires the explicit inclusion
of module.h when it was otherwise being included indirectly. Otherwise,
building zcache will fail.
Reported-by: NStephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: NThadeu Lima de Souza Cascardo <cascardo@holoscopio.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/staging/zcache/zcache-main.c

@@ -19,6 +19,7 @@
  *   http://marc.info/?l=linux-mm&m=127811271605009
  */
 
+#include <linux/module.h>
 #include <linux/cpu.h>
 #include <linux/highmem.h>
 #include <linux/list.h>