plat: stm32: update with libmaple

Commits merged (in timeline, latest first):

commit 0fca062e2d438bff98e26f6544299c69ec70b8ff
Author: Marti Bolivar <mbolivar@leaflabs.com>

	libmaple/usb/stm32f1/usb.c: cosmetics.

commit 07b56b89fba5e8f7e87781bfa03dedcf80356c43
Author: Marti Bolivar <mbolivar@leaflabs.com>

	libmaple/usb/stm32f1/usb.c: fix build error.