[source] ar71xx: fix legacy image build error

[LEDE Commits]

nbd pushed a commit to source.git, branch master:
https://git.lede-project.org/b1dbe6028eed57a89ae94c5e61e0b1e65f3aeb80

commit b1dbe6028eed57a89ae94c5e61e0b1e65f3aeb80
Author: Felix Fietkau <nbd at nbd.name>
AuthorDate: Sat Jan 7 21:00:47 2017 +0100

    ar71xx: fix legacy image build error
    
    Signed-off-by: Felix Fietkau <nbd at nbd.name>
---
 target/linux/ar71xx/image/legacy.mk | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/target/linux/ar71xx/image/legacy.mk b/target/linux/ar71xx/image/legacy.mk
index 3259016..f80b700 100644
--- a/target/linux/ar71xx/image/legacy.mk
+++ b/target/linux/ar71xx/image/legacy.mk
@@ -199,7 +199,7 @@ define Image/BuildLoader
 		LZMA_TEXT_START=0x80a00000 LOADADDR=0x80060000 \
 		LOADER_DATA="$(KDIR)/vmlinux$(5).bin.lzma" BOARD="$(1)" \
 		compile loader.$(2)
-	-$(CP) $(KDIR)/loader-$(1).$(2) $(KDIR)/loader-$(1)$(5).$(2)
+	-$(if $(5),$(CP) $(KDIR)/loader-$(1).$(2) $(KDIR)/loader-$(1)$(5).$(2))
 endef
 
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