fix warning about set and not used double
(this is not seen with 8c)

Reference: /n/atom/patch/applied2013/health6cwarn
Date: Wed Jun 19 04:06:39 CES 2013
Signed-off-by: quanstro@quanstro.net

--- /sys/src/cmd/disk/health/main.c	Wed Jun 19 04:06:25 2013
+++ /sys/src/cmd/disk/health/main.c	Wed Jun 19 04:06:25 2013
@@ -34,8 +34,6 @@
 	double life, used;
 	uchar cmd[10], buf[128];
 
-	life = 0;
-	used = 0;
 	memset(cmd, 0, sizeof(cmd));
         cmd[0] = OPlogsense;
         cmd[2] = LSstartstop|Cumulative;