Fix unsafe pointer conversion (#325)

Fix unsafe pointer conversion (#325)

Fix the following unsafe pointer conversion found using the Go 1.14
-d=checkptr gcflags (`go1.14rc1 test -gcflags=all=-d=checkptr -v ./...`)

```
fatal error: checkptr: unsafe pointer conversion

goroutine 68 [running]:
runtime.throw(0x5833e9, 0x23)
	runtime/panic.go:1112 +0x72 fp=0xc00030fba8 sp=0xc00030fb78 pc=0x432a32
runtime.checkptrAlignment(0xc00031f018, 0x544800, 0x1)
	runtime/checkptr.go:18 +0xb7 fp=0xc00030fbd8 sp=0xc00030fba8 pc=0x4063a7
github.com/fsnotify/fsnotify.(*Watcher).readEvents(0xc0002900f0)
	github.com/fsnotify/fsnotify/inotify.go:275 +0x457 fp=0xc00031ffd8 sp=0xc00030fbd8 pc=0x519037
runtime.goexit()
	runtime/asm_amd64.s:1375 +0x1 fp=0xc00031ffe0 sp=0xc00031ffd8 pc=0x463eb1
created by github.com/fsnotify/fsnotify.NewWatcher
	github.com/fsnotify/fsnotify/inotify.go:59 +0x1a5
```

Fixes #330