mm/cma: pair the trace_cma_alloc_start/finish

mm/cma: pair the trace_cma_alloc_start/finish

In the bad input validation cases, there is no trace_cma_alloc_finish to
match the trace_cma_alloc_start.  Move the trace_cma_alloc_start event
after the validations.

Link: https://lkml.kernel.org/r/20250605072532.972081-1-richardycc@google.com
Signed-off-by: Richard Chang <richardycc@google.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Kalesh Singh <kaleshsingh@google.com>
Cc: Martin Liu <liumartin@google.com>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>