microblaze: clean LDFLAGS to build kernel

Extra LDFLAGS from user space building may cause kernel failed
to compile.

Signed-off-by: Thomas Chou <thomas@wytron.com.tw>
Signed-off-by: Michal Simek <monstr@monstr.eu>
diff --git a/arch/microblaze/Makefile b/arch/microblaze/Makefile
index aaadfa7..ab731b7 100644
--- a/arch/microblaze/Makefile
+++ b/arch/microblaze/Makefile
@@ -36,6 +36,8 @@
 # r31 holds current when in kernel mode
 CFLAGS_KERNEL += -ffixed-r31 $(CPUFLAGS-1) $(CPUFLAGS-2)
 
+LDFLAGS		:=
+LDFLAGS_vmlinux	:=
 LDFLAGS_BLOB := --format binary --oformat elf32-microblaze
 
 LIBGCC := $(shell $(CC) $(CFLAGS_KERNEL) -print-libgcc-file-name)