wil6210: fix for 64-bit integer division

On some platforms, cycles_t is 64-bit, and gcc generates call to
__udivdi3 for straight division of cycles_t/cycles_t. This leads
to compilation failure, as this function is not exist in the kernel
runtime. do_div() to rescue

Original report:

tree:   git://git.kernel.org/pub/scm/linux/kernel/git/linville/wireless-next.git master
head:   2e91606f
commit: 7c0acf86 [81/103] wil6210: Tx performance monitoring
config: i386-randconfig-ha3-0620 (attached as .config)

All error/warnings:

   drivers/built-in.o: In function `wil_vring_debugfs_show':
>> debugfs.c:(.text+0x39b9be): undefined reference to `__udivdi3'
Signed-off-by: NVladimir Kondratiev <qca_vkondrat@qca.qualcomm.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/wil6210/debugfs.c

@@ -83,9 +83,10 @@ static int wil_vring_debugfs_show(struct seq_file *s, void *data)
 			char name[10];
 			/* performance monitoring */
 			cycles_t now = get_cycles();
-			cycles_t idle = txdata->idle;
+			cycles_t idle = txdata->idle * 100;
 			cycles_t total = now - txdata->begin;
 
+			do_div(idle, total);
 			txdata->begin = now;
 			txdata->idle = 0ULL;
 
@@ -93,7 +94,7 @@ static int wil_vring_debugfs_show(struct seq_file *s, void *data)
 
 			seq_printf(s, "\n%pM CID %d TID %d [%3d|%3d] idle %3d%%\n",
 				   wil->sta[cid].addr, cid, tid, used, avail,
-				   (int)((idle*100)/total));
+				   (int)idle);
 
 			wil_print_vring(s, wil, name, vring, '_', 'H');
 		}