MIPS: zboot: Remove copied source files on clean

The copied source files must be added to the extra-y list to have them
removed on clean.

Signed-off-by: Alban Bedel <albeu@free.fr>
Cc: Andrew Bresticker <abrestic@chromium.org>
Cc: Alex Smith <alex.smith@imgtec.com>
Cc: Wu Zhangjin <wuzhangjin@gmail.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/12233/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/boot/compressed/Makefile

@@ -41,6 +41,7 @@ endif
 
 vmlinuzobjs-$(CONFIG_KERNEL_XZ) += $(obj)/ashldi3.o $(obj)/bswapsi.o
 
+extra-y += ashldi3.c bswapsi.c
 $(obj)/ashldi3.o $(obj)/bswapsi.o: KBUILD_CFLAGS += -I$(srctree)/arch/mips/lib
 $(obj)/ashldi3.c $(obj)/bswapsi.c: $(obj)/%.c: $(srctree)/arch/mips/lib/%.c
 	$(call cmd,shipped)