fix:a compile bug in example/snake

[KrystalRay]

I tried to compile and run the snake example on Macos with the latest moonbit compiler(v0.6.24+012953835).
But i found some errors while compling.

Error: [4021]
    ╭─[ /Users/kelei/opensource/wasm4/function.mbt:22:3 ]
    │
 22 │   Sprite(bytes)
    │   ───┬──  
    │      ╰──── The value identifier Sprite is unbound.
────╯
Error: [4015]
    ╭─[ /Users/kelei/opensource/wasm4/function.mbt:60:26 ]
    │
 60 │   blit_ffi(get_addr(self.inner()), x, y, width, height, flags.to_int())
    │                          ──┬──  
    │                            ╰──── Type Sprite has no method inner.
────╯
Error: [4015]
    ╭─[ /Users/kelei/opensource/wasm4/function.mbt:82:19 ]
    │
 82 │     get_addr(self.inner()),
    │                   ──┬──  
    │                     ╰──── Type Sprite has no method inner.
────╯
error: failed to run build for target Wasm`

I think these may due to moonbit upgrade according to moonbit 月报

Please review my PR and consider to merge if it is helpful.