math/ceres-solver: don't use libs from USES=blaslapack

According to Ceres installation documentation:

... one needs to be careful to turn off the threading inside OpenBLAS
as it conflicts with use of threads in Ceres.

math/openblas exposes single-threaded (USE_THREAD=0) version as -lopenblas
while multi-threaded (NUM_THREADS=8) version as -lopenblasp (p suffix).