io/i2c: fix vet format error in test

Change-Id: I8b6eaab6eeb7117c7edd0ffbc314afeaf6f3e1b5
Reviewed-on: https://go-review.googlesource.com/78537
Reviewed-by: JBD <jbd@google.com>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/io/i2c/i2c_test.go b/io/i2c/i2c_test.go
index 77e3d17..8765e3e 100644
--- a/io/i2c/i2c_test.go
+++ b/io/i2c/i2c_test.go
@@ -22,10 +22,10 @@
 	for _, tt := range tc {
 		unmasked, tenbit := resolveAddr(tt.masked)
 		if want, got := tt.tenbitWant, tenbit; got != want {
-			t.Errorf("want address %b as 10-bit; got non 10-bit", want)
+			t.Errorf("want address %x as 10-bit; got non 10-bit", tt.masked)
 		}
 		if want, got := tt.addrWant, unmasked; got != want {
-			t.Errorf("want address %b; got %b", want, got)
+			t.Errorf("want address %v; got %v", want, got)
 		}
 	}
 }