libsecret: add patch to fix .pc file for static linking

The .pc file of libsecret needs to be adjusted to account for its
optional dependency on the gcrypt library. The patch has been
submitted upstream for inclusion.

Fixes:

  http://autobuild.buildroot.org/results/c2c/c2c6185cfbd9a0c91266c9e8a5f4221afb14930f/



Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>