zcache: Use div_u64 for 64-bit division

xv_get_total_size_bytes returns a u64 value and it's used in a division.
This causes build failures in 32-bit architectures, as reported by Randy
Dunlap.
Reported-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@holoscopio.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Dan Magenheimer <dan.magenheimer@oracle.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Acked-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/staging/zcache/zcache-main.c

@@ -28,6 +28,7 @@
 #include <linux/spinlock.h>
 #include <linux/types.h>
 #include <linux/atomic.h>
+#include <linux/math64.h>
 #include "tmem.h"
 
 #include "../zram/xvmalloc.h" /* if built in drivers/staging */
@@ -1162,6 +1163,7 @@ static void *zcache_pampd_create(char *data, size_t size, bool raw, int eph,
 	uint16_t client_id = get_client_id_from_client(cli);
 	unsigned long zv_mean_zsize;
 	unsigned long curr_pers_pampd_count;
+	u64 total_zsize;
 
 	if (eph) {
 		ret = zcache_compress(page, &cdata, &clen);
@@ -1194,8 +1196,9 @@ static void *zcache_pampd_create(char *data, size_t size, bool raw, int eph,
 		}
 		/* reject if mean compression is too poor */
 		if ((clen > zv_max_mean_zsize) && (curr_pers_pampd_count > 0)) {
-			zv_mean_zsize = xv_get_total_size_bytes(cli->xvpool) /
-						curr_pers_pampd_count;
+			total_zsize = xv_get_total_size_bytes(cli->xvpool);
+			zv_mean_zsize = div_u64(total_zsize,
+						curr_pers_pampd_count);
 			if (zv_mean_zsize > zv_max_mean_zsize) {
 				zcache_mean_compress_poor++;
 				goto out;