Documentation: fb: udlfb: clean up text and formatting

Clean up punctuation, spelling, and formatting for command line usage
and modprobe config file usage in udlfb.rst.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Bernie Thompson <bernie@plugable.com>
Cc: linux-fbdev@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Cc: Helge Deller <deller@gmx.de>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Cc: Bagas Sanjaya <bagasdotme@gmail.com>
Link: https://lore.kernel.org/r/20220828192501.14232-1-rdunlap@infradead.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>