Fix timespec.h documentation

There are 1,000,000,000 nanoseconds in a second.

Test: n/a
Change-Id: I8ce622ce3c60d7d5b06a056cfd0e6bea976b5aab
diff --git a/libc/include/bits/timespec.h b/libc/include/bits/timespec.h
index 0497cfe..daad03f 100644
--- a/libc/include/bits/timespec.h
+++ b/libc/include/bits/timespec.h
@@ -46,7 +46,7 @@
 struct timespec {
   /** Number of seconds. */
   time_t tv_sec;
-  /** Number of nanoseconds. Must be less than 1,000,000. */
+  /** Number of nanoseconds. Must be less than 1,000,000,000. */
   long tv_nsec;
 };
 #endif