libssh2: fix library search path issues

Fix issues with some toolchains not finding libssl or libgcrypt.

Fixes http://autobuild.buildroot.net/results/eeaaf41c0c5f88357af8445750dce776774c2b5d
Fixes http://autobuild.buildroot.net/results/7a2590a7c3a1f52590f3e886b7cf9d04ad966a10



[Peter: indentation fixup]
Signed-off-by: Ryan Barnett <rjbarnet@rockwellcollins.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>