Fix a spelling error in a comment

fs/vfs/fs_poll.c

@@ -176,7 +176,7 @@ static inline int poll_setup(FAR struct pollfd *fds, nfds_t nfds, sem_t *sem)
                   (void)poll_fdsetup(fds[j].fd, &fds[j], false);
                 }
 
-              /* Indicate an error on the file discriptor */
+              /* Indicate an error on the file descriptor */
 
               fds[i].revents |= POLLERR;
               return ret;