virSecurityDACSetSecurityImageLabel: Unmark @def as unused

The @def is clearly used just a few lines below. There's no need to use
ATTRIBUTE_UNUSED for it.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

src/security/security_dac.c

@@ -342,7 +342,7 @@ virSecurityDACSetSecurityFileLabel(virDomainDiskDefPtr disk ATTRIBUTE_UNUSED,
 
 static int
 virSecurityDACSetSecurityImageLabel(virSecurityManagerPtr mgr,
-                                    virDomainDefPtr def ATTRIBUTE_UNUSED,
+                                    virDomainDefPtr def,
                                     virDomainDiskDefPtr disk)
 
 {