libpayload: Add in a missing "static".

The readwrite_chunk was private to the usb mass storage driver, but wasn't
marked as static which was upsetting the compiler.

Change-Id: I0ef5c5f96a29f793dd43ff672a939902bad13c45
Signed-off-by: Gabe Black <gabeblack@google.com>
Reviewed-on: https://chromium-review.googlesource.com/169816
Reviewed-by: Julius Werner <jwerner@chromium.org>
Commit-Queue: Gabe Black <gabeblack@chromium.org>
Tested-by: Gabe Black <gabeblack@chromium.org>
(cherry picked from commit 8140e6145b3d072b7f12a924418570022207c065)
Signed-off-by: Isaac Christensen <isaac.christensen@se-eng.com>
Reviewed-on: http://review.coreboot.org/6648
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>
diff --git a/payloads/libpayload/drivers/usb/usbmsc.c b/payloads/libpayload/drivers/usb/usbmsc.c
index 1f8c551..464d73d 100644
--- a/payloads/libpayload/drivers/usb/usbmsc.c
+++ b/payloads/libpayload/drivers/usb/usbmsc.c
@@ -365,7 +365,7 @@
  * @param buf buffer to read into or write from. Must be at least n*sectorsize bytes
  * @return 0 on success, 1 on failure
  */
-int
+static int
 readwrite_chunk (usbdev_t *dev, int start, int n, cbw_direction dir, u8 *buf)
 {
 	cmdblock_t cb;