p11-kit: fix detection of certificates path

p11-kit: fix detection of certificates path

The p11-kit configure script looked for certificates location on the
host. This doesn't work well with cross compilation. Make the
certificates patch depend on BR2_PACKAGE_CA_CERTIFICATES, and set the
right target location of the path.

Fixes:
http://autobuild.buildroot.net/results/295/295614d4aa3db9bb35bebbe56e38110f5a2de178/
http://autobuild.buildroot.net/results/0fb/0fb454ca0df74a8585cffe8f5d1f5d23cdfdbec6/
http://autobuild.buildroot.net/results/ef7/ef71f3d67afba547b5167253fb02476e59152803/

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>