[source] build: fix image builder profile override (FS#55)

[LEDE Commits]

nbd pushed a commit to source.git, branch master:
https://git.lede-project.org/?p=source.git;a=commitdiff;h=ed90d50bc4cbbcf615f880c1799814ccf743de8c

commit ed90d50bc4cbbcf615f880c1799814ccf743de8c
Author: Felix Fietkau <nbd at nbd.name>
AuthorDate: Thu Jul 21 13:27:12 2016 +0200

    build: fix image builder profile override (FS#55)
    
    Signed-off-by: Felix Fietkau <nbd at nbd.name>
---
 include/target.mk | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/target.mk b/include/target.mk
index 6a0ec97..427708e 100644
--- a/include/target.mk
+++ b/include/target.mk
@@ -91,7 +91,7 @@ else
   endef
 endif
 
-PROFILE:=$(call qstrip,$(CONFIG_TARGET_PROFILE))
+PROFILE?=$(call qstrip,$(CONFIG_TARGET_PROFILE))
 
 ifeq ($(TARGET_BUILD),1)
   ifneq ($(DUMP),)