[Coverage] Apply filtered paths to summary

Summary:
The script to generate code coverage reports supports passing filter paths to llvm-cov when generating the HTML reports, but doesn't pass those paths to the summary generation as well. This results in a summary report that doesn't match the HTML report.

This patch addresses the problem by also passing the filter paths to the summary report generation.

Reviewers: vsk

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D53110

llvm-svn: 344217