audit: rename the misleading audit_get_context() to audit_take_context()

"get" usually implies incrementing a refcount into a structure to indicate a
reference being held by another part of code.

Change this function name to indicate it is in fact being taken from it,
returning the value while clearing it in the supplying structure.

Signed-off-by: Richard Guy Briggs <rgb@redhat.com>

diff --cc kernel/auditsc.c
Simple merge