firewire: firewire-cdev.hL get rid of a docs warning

firewire: firewire-cdev.hL get rid of a docs warning

This warning:

	./include/uapi/linux/firewire-cdev.h:312: WARNING: Inline literal start-string without end-string.

is because %FOO doesn't work if there's a parenthesis at the
string (as a parenthesis may indicate a function). So, mark
the literal block using the alternate ``FOO`` syntax.

Acked-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/9b2501a41eba27ccdd4603cac2353c0efba7a90a.1586881715.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>