Use correct variable name for value to convert.

Note by @antirez: this code was never compiled because utils.c lacked the
float.h include, so we never noticed this variable was mispelled in the
past.

This should provide a noticeable speed boost when saving certain types
of databases with many sorted sets inside.

src/util.c

@@ -7,6 +7,7 @@
 #include <math.h>
 #include <unistd.h>
 #include <sys/time.h>
+#include <float.h>
 
 #include "util.h"
 
@@ -319,7 +320,7 @@ int d2string(char *buf, size_t len, double value) {
          * integer printing function that is much faster. */
         double min = -4503599627370495; /* (2^52)-1 */
         double max = 4503599627370496; /* -(2^52) */
-        if (val > min && val < max && value == ((double)((long long)value)))
+        if (value > min && value < max && value == ((double)((long long)value)))
             len = ll2string(buf,len,(long long)value);
         else
 #endif