liburing: Simplify CFLAGS assignment for MUSL targets

- Simplify the way we deal with additional CFLAGS for MUSL targets

Signed-off-by: Christian Lachner <gladiac@gmail.com>

libs/liburing/Makefile

@@ -33,9 +33,7 @@ endef
 
 CONFIGURE_ARGS:=--prefix=$(CONFIGURE_PREFIX) --cc=${TARGET_CC}
 
-ifeq ($(CONFIG_USE_MUSL),y)
-	TARGET_CFLAGS+=-Dloff_t=off_t
-endif
+TARGET_CFLAGS += $(if $(CONFIG_USE_MUSL),-Dloff_t=off_t)
 
 define Build/Compile
 	$(MAKE) $(PKG_BUILD_DIR) \