[CSSPGO] Always use callsite samples as callsite probe counts.

For CS profile, the callsite count of previously inlined callees is populated with the entry count of the callees. Therefore when trying to get a weight for calliste probe after inlinining, the callsite count should always be used. The same fix has already been made for non-probe case.

Reviewed By: wenlei

Differential Revision: https://reviews.llvm.org/D98094