unix: add race annotations to Pread and Pwrite

Follow CL 391954 which changed Pread/Pwrite in package syscall.

For golang/go#51618

Change-Id: Icc587c61f083886bb66ca96717f686f56b398e34
Reviewed-on: https://go-review.googlesource.com/c/sys/+/392794
Trust: Tobias Klauser <tobias.klauser@gmail.com>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/unix/syscall_linux_mips64x.go b/unix/syscall_linux_mips64x.go
index f0b1380..98a2660 100644
--- a/unix/syscall_linux_mips64x.go
+++ b/unix/syscall_linux_mips64x.go
@@ -21,8 +21,8 @@
 //sys	Lchown(path string, uid int, gid int) (err error)
 //sys	Listen(s int, n int) (err error)
 //sys	Pause() (err error)
-//sys	Pread(fd int, p []byte, offset int64) (n int, err error) = SYS_PREAD64
-//sys	Pwrite(fd int, p []byte, offset int64) (n int, err error) = SYS_PWRITE64
+//sys	pread(fd int, p []byte, offset int64) (n int, err error) = SYS_PREAD64
+//sys	pwrite(fd int, p []byte, offset int64) (n int, err error) = SYS_PWRITE64
 //sys	Renameat(olddirfd int, oldpath string, newdirfd int, newpath string) (err error)
 //sys	Seek(fd int, offset int64, whence int) (off int64, err error) = SYS_LSEEK