[msan] Nit: use init_origins parameter instead of __msan_get_track_origins() in InitShadowWithReExec (#86994)

This fixes a nit I had accidentally introduced in
https://github.com/llvm/llvm-project/pull/85142

I don't think the value of __msan_get_track_origins() will change
between the start and end of InitShadowWithReExec, but it's cleaner to
use the parameter.

GitOrigin-RevId: dc0cb17241aeff205a0c3a7cc4e790afab7484dd
1 file changed