fixed 9fdb80f8 from https://gitee.com/harylee/kernel_liteos_a/pulls/628

fix: 共享内存问题修复
Signed-off-by: NHaryslee <lihao189@huawei.com>
背景：父进程移除共享内存并标记SHM_SEG_REMOVE,当子进程资源回收时在
ShmFindSeg接口中判断该共享内存具有SHM_SEG_REMOVE时返回空，但是此时
seg->ds.shm_nattch不为0，不应返回空。
方案：ShmFindSeg接口中增加seg->ds.shm_nattch为0的判断。

close #I47X2Z

Change-Id: I8735cd11ac237b17fa745c50313da0fd0649bb9f

kernel/base/vm/shm.c

@@ -304,7 +304,7 @@ STATIC struct shmIDSource *ShmFindSeg(int shmid)
     }
 
     seg = &g_shmSegs[shmid];
-    if ((seg->status & SHM_SEG_FREE) || (seg->status & SHM_SEG_REMOVE)) {
+    if ((seg->status & SHM_SEG_FREE) || ((seg->ds.shm_nattch == 0) && (seg->status & SHM_SEG_REMOVE))) {
         set_errno(EIDRM);
         return NULL;
     }