port.c: MagAtof() constify and add prototype

utils/port.c

@@ -42,7 +42,7 @@ static char rcsid[] __attribute__ ((unused)) = "$Header: /usr/cvsroot/magic-8.0/
 
 float
 MagAtof(s)
-    char *s;
+    const char *s;
 {
 #ifdef linux
     float flt;

utils/utils.h

@@ -103,7 +103,7 @@ extern gzFile flock_zopen();
  */
 #define	LAST_BIT_OF(x)	((x) & ~((x) - 1))
 
-extern float MagAtof();
+extern float MagAtof(const char *s);
 
 extern int Wait(int *status);
 extern int WaitPid(int pid, int *status);