image: don't mask imagesize failures

On a failed image-size check, Build/check-size currently prints an error
message, removes the offending build file, and returns success to the build
system, which is problematic for a few reasons. Returning success lets the
overall build complete without flagging the error, unless a user happens
to search through logs. It also allows subsequent build steps to run, which
can fail in various ways due to the target file's removal, and result in
broken image files (e.g. only a header/footer present).

Update check-size to return failure as needed and avoid these problems.

Signed-off-by: Tony Ambardar <itugrok@yahoo.com>

include/image-commands.mk

@@ -223,6 +223,7 @@ define Build/check-size
 	[ $$limitsize -ge $$imagesize ] || { \
 		$(call ERROR_MESSAGE,    WARNING: Image file $@ is too big: $$imagesize > $$limitsize); \
 		rm -f $@; \
+		return 1; \
 	}
 endef