scripts: get_abi.pl: fix parsing on ReST mode

When the source ABI file is using ReST notation, the script
should handle whitespaces and lines with care, as otherwise
the file won't be properly recognized.

Address the bugs that are on such part of the script.

Acked-by: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/5c22c54fbd0cda797b691d52c568be6d0d1079d8.1604042072.git.mchehab+huawei@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>