unix: fix staticcheck issues

Change-Id: If7abd7a743c4359a9780401cec7c874d530ee268
Reviewed-on: https://go-review.googlesource.com/c/sys/+/396674
Trust: Matt Layher <mdlayher@gmail.com>
Run-TryBot: Matt Layher <mdlayher@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/unix/internal/mkmerge/mkmerge_test.go b/unix/internal/mkmerge/mkmerge_test.go
index 3207244..e61d7d4 100644
--- a/unix/internal/mkmerge/mkmerge_test.go
+++ b/unix/internal/mkmerge/mkmerge_test.go
@@ -410,6 +410,10 @@
 		}
 
 		got, err := filter(inFiles[0].src, commonSet.keepCommon)
+		if err != nil {
+			t.Fatal(err)
+		}
+
 		expected := []byte(mergedFile)
 
 		if !bytes.Equal(got, expected) {
diff --git a/unix/syscall_freebsd_test.go b/unix/syscall_freebsd_test.go
index 0841148..de02a1a 100644
--- a/unix/syscall_freebsd_test.go
+++ b/unix/syscall_freebsd_test.go
@@ -221,14 +221,14 @@
 		panic(fmt.Sprintf("CapRightsIsSet failed: %s %#v", err, err))
 	}
 	if !b {
-		panic(fmt.Sprintf("Unexpected rights"))
+		panic("Unexpected rights")
 	}
 	b, err = unix.CapRightsIsSet(r, []uint64{unix.CAP_READ, unix.CAP_LOOKUP, unix.CAP_WRITE})
 	if err != nil {
 		panic(fmt.Sprintf("CapRightsIsSet failed: %s %#v", err, err))
 	}
 	if b {
-		panic(fmt.Sprintf("Unexpected rights (2)"))
+		panic("Unexpected rights (2)")
 	}
 
 	// Can no longer create a file