package/p11-kit: fix build without tasn1

package/p11-kit: fix build without tasn1

Commit d82da39d55ea16c3c8aa3c5a8ea91fd6c2ceafbb forgot to move
BR2_PACKAGE_CA_CERTIFICATES condition under BR2_PACKAGE_LIBTASN1 to
avoid the following build failure:

checking if trust module is enabled... configure: WARNING: --with-libtasn1 is needed in order to build the trust module, disabling
no
checking for trust module paths... configure: error: need --enable-trust-module in order to specify trust module paths.

Fixes:
 - http://autobuild.buildroot.org/results/e7f68205e1b776f9af34e6017f6eb17f46aa2f19

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>