libpayload: usb: Retry get_descriptor() on failure

libpayload: usb: Retry get_descriptor() on failure

Certain Lexar USB disks may fail during the first calls to
get_descriptor(..., DT_CFG, ...) for unknown reasons. Therefore, make
several attempts before giving up.

BUG=chromium:466758
TEST=Manual on Samus. Go to recovery mode, verify that Lexar LJDS70 USB
stick is bootable.
BRANCH=None

Change-Id: I476ac22f9c4f844c60ebc6e53af8c144d70bb9d4
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Original-Commit-Id: 93a0570b343479dd22506ad4d7961f0ea4251f8c
Original-Signed-off-by: Shawn Nematbakhsh <shawnn@chromium.org>
Original-Change-Id: Ie581c7c71c53816065c7f59202581888a79e445e
Original-Reviewed-on: https://chromium-review.googlesource.com/302403
Original-Commit-Ready: Shawn N <shawnn@chromium.org>
Original-Tested-by: Shawn N <shawnn@chromium.org>
Original-Reviewed-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: http://review.coreboot.org/12133
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>