update_passwd: fix context variable

Commit
https://git.busybox.net/busybox/commit/libbb/update_passwd.c?id=2496616b0a8d1c80cd1416b73a4847b59b9f969a

changed the variable used from context to seuser but forgot this
change resulting in build errors detected by buildroot autobuilders:

http://autobuild.buildroot.net/results/b89/b89b7d0f0601bb706e76cea31cf4e43326e5540c//build-end.log

libbb/update_passwd.c:51:11: error: 'context' undeclared (first use in
 this function); did you mean 'ucontext'?
   freecon(context);

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/libbb/update_passwd.c b/libbb/update_passwd.c
index 7b67f30..a228075 100644
--- a/libbb/update_passwd.c
+++ b/libbb/update_passwd.c
@@ -48,7 +48,7 @@
 			bb_simple_error_msg_and_die("SELinux: access denied");
 	}
 	if (ENABLE_FEATURE_CLEAN_UP)
-		freecon(context);
+		freecon(seuser);
 }
 #else
 # define check_selinux_update_passwd(username) ((void)0)