Fix sff panic deadlock, share the evdev probe, assorted review cleanups

init.go

@@ -7,6 +7,8 @@ import (
 	"time"
 
 	"golang.org/x/sys/unix"
+
+	"g.fc.run/theater/cabletest/internal/evdev"
 )
 
 // Running as PID 1 there is nothing underneath us: sysfs and devtmpfs are what
@@ -129,9 +131,9 @@ func waitForTouchscreen() checkResult {
 	res := checkResult{item: "touchscreen"}
 	start := time.Now()
 	for {
-		f, err := findTouchscreen()
+		ts, err := evdev.FindTouchscreen(os.O_RDONLY)
 		if err == nil {
-			f.Close()
+			ts.F.Close()
 			waited := time.Since(start)
 			if waited < touchPoll {
 				res.state = "ready"