Documentation: arm: remove hyphen from BG2Q in Marvell Berlin docs

The chip's design name isn't hyphenated anywhere else, and none of the
other names in the same document are hyphenated.

Signed-off-by: Thomas Hebb <tommyhebb@gmail.com>
Acked-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>