Type inconsistent between struct dirent's inum(ushort) and its usage(uint). about xv6-riscv

[zhouzilong2020]

Since each dinode has 64 bytes right now, and there are 13 blocks for inode on disk, xv6 chould at most have 208 inode.

To make the data type of inum consistent, I suggest:

1. Changing struct dirent as follows:

#define DIRSIZ 12
struct dirent {
  uint inum;
  char name[DIRSIZ];
};

2. Changing inum to ushort everywhere, which includes much more modifications to the code.