seqlock: Remove atomic_init to fix compilation error.

Since the adafruit-kb2040:smp do not support the `atomic_init`, we have
to remove the function.

Signed-off-by: ouyangxiangzhen <ouyangxiangzhen@xiaomi.com>

include/nuttx/seqlock.h

@@ -66,10 +66,9 @@ extern "C"
 
 static inline_function void seqlock_init(FAR seqcount_t *s)
 {
-#ifdef CONFIG_SMP
-  atomic_init((FAR atomic_t *)&s->sequence, 0u);
-#else
   s->sequence = 0u;
+#ifdef CONFIG_SMP
+  SMP_WMB();
 #endif
 }