hv:enable the O2 option for HV
commit removed O2 option improperly,
this patch re-enable it.
@@ -74,6 +74,7 @@ CFLAGS += -m64 -mno-mmx -mno-sse -mno-sse2 -mno-80387 -mno-fp-ret-in-387
CFLAGS += -mno-red-zone
CFLAGS += -nostdinc -nostdlib -fno-common
CFLAGS += -Werror
+CFLAGS += -O2
ifeq (y, $(CONFIG_RELOC))
CFLAGS += -fpie
else
