POSIX strerror_r returns an error number, not -1

The posix spec says strerror_r returns a positive error number,  not
-1 and set errno.

Test: bionic-unit-tests-static
Change-Id: I6a12d50d046f9caac299bf3bff63e6c9496c1b6f
diff --git a/libc/bionic/strerror.cpp b/libc/bionic/strerror.cpp
index 5733567..0deb200 100644
--- a/libc/bionic/strerror.cpp
+++ b/libc/bionic/strerror.cpp
@@ -196,8 +196,7 @@
     length = async_safe_format_buffer(buf, buf_len, "Unknown error %d", error_number);
   }
   if (length >= buf_len) {
-    errno_restorer.override(ERANGE);
-    return -1;
+    return ERANGE;
   }
 
   return 0;