zram: fix warning of print format

kbuild bot whinges due to print format mistmatch caused by
zram: force disksize setting before using zram.

This patch fixes it.
Reported-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/zram/zram_drv.c

@@ -519,7 +519,7 @@ int zram_init_device(struct zram *zram)
 		"ratio. Note that zram uses about 0.1%% of the size of "
 		"the disk when not in use so a huge zram is "
 		"wasteful.\n"
-		"\tMemory Size: %zu kB\n"
+		"\tMemory Size: %lu kB\n"
 		"\tSize you selected: %llu kB\n"
 		"Continuing anyway ...\n",
 		(totalram_pages << PAGE_SHIFT) >> 10, zram->disksize >> 10