Fix vmstat(8) warnings

[Brian Callahan]

Hi tech --

Silence a pair of -Wshadow warnings caught by WARNINGS=yes.

~Brian

Index: dkstats.c
===================================================================
RCS file: /cvs/src/usr.bin/vmstat/dkstats.c,v
retrieving revision 1.39
diff -u -p -u -p -r1.39 dkstats.c
--- dkstats.c   4 Sep 2016 14:21:05 -0000       1.39
+++ dkstats.c   29 May 2017 21:20:26 -0000
@@ -201,9 +201,9 @@ dkreadstats(void)
                            (name = strsep(&bufpp, ",")) != NULL; i++)
                                dk_name[i] = name;
                        for (i = 0; i < dk_ndrive; i++) {
-                               char *p = strchr(dk_name[i], ':');
-                               if (p)
-                                       *p = '\0';
+                               char *ep = strchr(dk_name[i], ':');
+                               if (ep)
+                                       *ep = '\0';
                        }
                        disknames = cur.dk_name[0];     /* To free old names. */
 
@@ -534,9 +534,9 @@ dkinit(int sel)
                        cur.dk_select[i] = sel;
                }
                for (i = 0; i < dk_ndrive; i++) {
-                       char *p = strchr(cur.dk_name[i], ':');
-                       if (p)
-                               *p = '\0';
+                       char *ep = strchr(cur.dk_name[i], ':');
+                       if (ep)
+                               *ep = '\0';
                }
        } else {
 #if !defined(NOKVM)