audit: change decimal constant to macro for invalid uid

SFR reported this 2013-05-15:

> After merging the final tree, today's linux-next build (i386 defconfig)
> produced this warning:
>
> kernel/auditfilter.c: In function 'audit_data_to_entry':
> kernel/auditfilter.c:426:3: warning: this decimal constant is unsigned only
> in ISO C90 [enabled by default]
>
> Introduced by commit 780a7654cee8 ("audit: Make testing for a valid
> loginuid explicit") from Linus' tree.

Replace this decimal constant in the code with a macro to make it more readable
(add to the unsigned cast to quiet the warning).

Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Eric Paris <eparis@redhat.com>
diff --git a/kernel/auditfilter.c b/kernel/auditfilter.c
index f7aee8b..8a344ce 100644
--- a/kernel/auditfilter.c
+++ b/kernel/auditfilter.c
@@ -423,7 +423,7 @@
 		f->lsm_rule = NULL;
 
 		/* Support legacy tests for a valid loginuid */
-		if ((f->type == AUDIT_LOGINUID) && (f->val == ~0U)) {
+		if ((f->type == AUDIT_LOGINUID) && (f->val == AUDIT_UID_UNSET)) {
 			f->type = AUDIT_LOGINUID_SET;
 			f->val = 0;
 		}