Fix format-string error in delocate.go.

Errorf treats its argument as a format string and so “%rax” is a
problem.

Change-Id: I863ef361f07d0b8a348994efe45869202d0b31f1
Reviewed-on: https://boringssl-review.googlesource.com/24944
Reviewed-by: Steven Valdez <svaldez@google.com>
Commit-Queue: Steven Valdez <svaldez@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
diff --git a/util/fipstools/delocate.go b/util/fipstools/delocate.go
index 2c1ba49..b4371fc 100644
--- a/util/fipstools/delocate.go
+++ b/util/fipstools/delocate.go
@@ -1038,7 +1038,7 @@
 					targetReg = d.contents(argNodes[1])
 					wrappers = append(wrappers, finalTransform(d.output, instructionName, targetReg))
 					if isValidLEATarget(targetReg) {
-						return nil, fmt.Errorf("Currently transforming moves are assumed to target XMM registers. Otherwise we'll pop %rax before reading it to do the transform.")
+						return nil, errors.New("Currently transforming moves are assumed to target XMM registers. Otherwise we'll pop %rax before reading it to do the transform.")
 					}
 				default:
 					return nil, fmt.Errorf("Cannot rewrite GOTPCREL reference for instruction %q", instructionName)