package/pinentry: fix include paths

The pinentry tarball contains generated .moc files that contains
incorrect include paths: they are probably specific to the machine of
the user who generated the tarball.

Fix those paths.

Fixes numerous autobuild failures:
    http://autobuild.buildroot.org/results/96c/96c68e9a6c528e15016cb10f0f73e52f58815bec/
    http://autobuild.buildroot.org/results/50e/50ecb6b347ab4970c701b1aed7b42518fef9a52c/
    http://autobuild.buildroot.org/results/fcb/fcbe8b971ef37c0e7c458bc32295a89be9872b61/


    ...

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>