freedreno: Add missing va_end.
Fix warning reported by Coverity Scan.
Missing varargs init or cleanup (VARARGS)
missing_va_end: va_end was not called for ap.
Fixes: a0ca1462f317 ("freedreno: add logging infrastructure")
Signed-off-by: Vinson Lee <vlee@freedesktop.org>
cc: @robclark