cad/opencascade: fix cmake files

A cmake macro, which should have configured $OCCT_INSTALL_BIN_LETTER was
not applied correctly. Thus some cmake files where badly configured, and
some consumers could not use them.

PR: 266280
Reported by: yuri
MFH: 2022Q3

(cherry picked from commit 31735a5b1aae9a7967e8cc5f12ffab7779acc53c)