csky: syscache: Fixup duplicate cache flush

The current csky logic of sys_cacheflush is wrong, it'll cause
icache flush call dcache flush again. Now fixup it with a
conditional "break & fallthrough".

Fixes: 997153b9a7 ("csky: Add flush_icache_mm to defer flush icache all")
Fixes: 0679d29d3e ("csky: fix syscache.c fallthrough warning")
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Co-Developed-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Cc: Arnd Bergmann <arnd@arndb.de>

arch/csky/mm/syscache.c

@@ -12,15 +12,17 @@ SYSCALL_DEFINE3(cacheflush,
 		int, cache)
 {
 	switch (cache) {
-	case ICACHE:
 	case BCACHE:
-		flush_icache_mm_range(current->mm,
-				(unsigned long)addr,
-				(unsigned long)addr + bytes);
-		fallthrough;
 	case DCACHE:
 		dcache_wb_range((unsigned long)addr,
 				(unsigned long)addr + bytes);
+		if (cache != BCACHE)
+			break;
+		fallthrough;
+	case ICACHE:
+		flush_icache_mm_range(current->mm,
+				(unsigned long)addr,
+				(unsigned long)addr + bytes);
 		break;
 	default:
 		return -EINVAL;