jasper: disable PDF documentation generation

jasper: disable PDF documentation generation

We don't need the PDF document on target. This also avoids incompatible host
Latex packages.

Fixes:
http://autobuild.buildroot.net/results/e60/e60c4a71a08aebadd0bc3fb95a57a4a223e4b6fa/
http://autobuild.buildroot.net/results/4ec/4ec8a1735590a3cad4b74630b4b6bdd2e3a7eec8/

[Peter: reformat as suggested by Yann]
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>