Change description of dev_boot_usb

Now indicates it covers SD as well (it did already, but now it's clearer).

BUG=chromium-os:17907
TEST=run `crossystem`; look at new descriptions

Change-Id: I4e4d8502b0dc5a29eb403039535b7512941ab4fa
Reviewed-on: http://gerrit.chromium.org/gerrit/4408
Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Randall Spangler <rspangler@chromium.org>
1 file changed