ti-utils: link with pthread to avoid build failure

Add '-lpthread' option to LIBS in ti-utils.mk file
to link this package with pthread

Fixes:
http://autobuild.buildroot.net/results/132/132072d849a3ec572aa80e51833bf6906a54400a//



Signed-off-by: Yuvaraj Patil <yuvaraj.patil@wipro.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>