nds32: Remove gcc unused option

-G0 is an old option, not support now,
So remove it.
It can help to fix compile error when
build with nds32 pre-build toolchain.

Signed-off-by: Rick Chen <rick@andestech.com>
Cc: Greentime Hu <greentime@andestech.com>
diff --git a/arch/nds32/config.mk b/arch/nds32/config.mk
index 12cec36..a0f14ae 100644
--- a/arch/nds32/config.mk
+++ b/arch/nds32/config.mk
@@ -17,6 +17,6 @@
 
 PLATFORM_RELFLAGS	+= -fno-common -mrelax
 PLATFORM_RELFLAGS	+= -gdwarf-2
-PLATFORM_CPPFLAGS	+= -D__nds32__ -G0 -ffixed-10 -fpie
+PLATFORM_CPPFLAGS	+= -D__nds32__ -ffixed-10 -fpie
 
 LDFLAGS_u-boot		= --gc-sections --relax -pie