vmstat: precision issues in unitConvert()

Fix conversion errors due to precision issues in function unitConvert

For example: unitConvert(98720620) will return 98720624, not 98720620.

Because we do (unsigned long)(float)98720620 in function unitConvert
and this is wrong! We should do (unsigned long)(double)98720620 here.

Signed-off-by: Craig Small <csmall@dropbear.xyz>

References:
 procps-ng/procps!75

src/vmstat.c

@@ -336,8 +336,8 @@ static void new_header(void)
 
 static unsigned long unitConvert(unsigned long size)
 {
-    float cvSize;
-    cvSize = (float)size / dataUnit * ((statMode == SLABSTAT) ? 1 : 1024);
+    double cvSize;
+    cvSize = (double)size / dataUnit * ((statMode == SLABSTAT) ? 1 : 1024);
     return ((unsigned long)cvSize);
 }