Fix r231300: Use correct test so we only bail out on error instead of on non-error.

Also, fix a style bug.

Submitted by:	ache
Approved by:	cperciva
MFC after:	1 month

usr.sbin/pkg_install/create/perform.c

@@ -216,7 +216,7 @@ pkg_perform(char **pkgs)
     /* Prefix should add an @cwd to the packing list */
     if (Prefix) {
         char resolved_prefix[PATH_MAX];
-        if (realpath(Prefix, resolved_prefix) != 0)
+        if (realpath(Prefix, resolved_prefix) == NULL)
 	    err(EXIT_FAILURE, "couldn't resolve path for prefix: %s", Prefix);
 	add_plist_top(&plist, PLIST_CWD, resolved_prefix);
     }