usb_charge: fix various typos and doxygen tags
usb_charge: fix various typos and doxygen tags

Various typo/doxygen fixes in usb_charge.h.

BRANCH=none
BUG=none
TEST=zmake testall

Signed-off-by: Fabio Baltieri <1c55e39c05d9ab42261288cf330256b2af6ba179@google.com>
Change-Id: I15b73a1533eb7be945d5c51a9c4b45e823c5ad2a
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3661582
Reviewed-by: Wai-Hong Tam <04b587fdf5845741a0c5a8b9cd59ca72d73ef8fc@google.com>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec