kernel/semaphore: update some comments on nsem_inode_s
Add more description on some field of struct nsem_inode_s.
[Shin: backported from NuttX]
struct inode;
struct nsem_inode_s {
+ /*
+ * This must be the first element of the structure. In sem_close()
+ * this structure must be cast compatible with sem_t.
+ */
sem_t ns_sem; /* The contained semaphore */
/* Inode payload unique to named semaphores */
