Documentation: HID: hiddev editing & corrections

Do basic editing & correction to hiddev.rst:
- use HID instead of hid consistently
- add hyphenation of multi-word adjectives
- drop a duplicate word
- unhyphenate "a priori"

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Jiri Kosina <jikos@kernel.org>
Cc: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Cc: linux-input@vger.kernel.org
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Cc: Jonathan Cameron <jic23@kernel.org>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>