scripts/get_abi: change the file/line number meta info

In order to make it more standard and ReST compatible,
change the meta-tag used with --enable-lineno from:

	#define LINENO

to
	.. LINENO

In practice, no functional changes.

Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>
Link: https://lore.kernel.org/r/125ffd31fbc77ad9eee4d6906e1830b8162fa6ca.1648290305.git.mchehab@kernel.org


Signed-off-by: Jonathan Corbet <corbet@lwn.net>