Documentation: usb: gadget: Wrap remaining usage snippets in literal code block

Documentation: usb: gadget: Wrap remaining usage snippets in literal code block

Several configfs usage snippets forget to be formatted as literal code
blocks. These were outputted in htmldocs output as normal paragraph
instead. In particular, snippet for custom string descriptors as added
in 15a7cf8caabee4 ("usb: gadget: configfs: Support arbitrary string
descriptors") is shown as single combined paragraph, rather than two
command lines.

Wrap them like the rest of snippets.

Fixes: 5e654a4655c3 ("Documentation/usb: gadget_configfs")
Fixes: d80b5005c5dd ("docs: usb: convert documents to ReST")
Fixes: 15a7cf8caabe ("usb: gadget: configfs: Support arbitrary string descriptors")
Signed-off-by: Bagas Sanjaya <bagasdotme@gmail.com>
Acked-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Link: https://lore.kernel.org/r/20250610031705.32774-2-bagasdotme@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>