selftests: Makefile: clear LDFLAGS for make O=dir use-case

kselftest target fails when object directory is specified to relocate
objects. Inherited "LDFLAGS = -m" fails the test builds. Clear it.
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>

tools/testing/selftests/Makefile

@@ -52,6 +52,10 @@ override LDFLAGS =
 override MAKEFLAGS =
 endif
 
+ifneq ($(KBUILD_SRC),)
+override LDFLAGS =
+endif
+
 BUILD := $(O)
 ifndef BUILD
   BUILD := $(KBUILD_OUTPUT)