apple/glx/log: added missing va_end() after va_copy()

Each invocation of va_copy() must be matched by a
corresponding invocation of va_end()

Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>
Fixes: 51691f07 "darwin: Use ASL for logging"
Signed-off-by: Andrii Simiklit <andrii.simiklit@globallogic.com>
(cherry picked from commit 267ed292)