Fix incorrect initial value of __kmp_affinity_type.

Affinity initialization code expects __kmp_affinity_type has the value
affinity_default by default, but the cleanup code does not properly set the
value back to affinity_default.  This may introduce some issues when multiple
roots are trying to initialize/uninitialize the runtime successively.

Patch by Hansang Bae

Differential Revision: https://reviews.llvm.org/D31012

llvm-svn: 298313