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_arm.go b/unix/syscall_linux_arm.go
index 343c91f..c1a7778 100644
--- a/unix/syscall_linux_arm.go
+++ b/unix/syscall_linux_arm.go
@@ -96,8 +96,8 @@
 
 //sys	utimes(path string, times *[2]Timeval) (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	Truncate(path string, length int64) (err error) = SYS_TRUNCATE64
 //sys	Ftruncate(fd int, length int64) (err error) = SYS_FTRUNCATE64