perf tools: Fix compile error on sample->user_regs

perf tools: Fix compile error on sample->user_regs

It's recently changed to allocate dynamically but misses to update some
arch-dependent codes to use perf_sample__user_regs().

Fixes: dc6d2bc2d893a878 ("perf sample: Make user_regs and intr_regs optional")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Reviewed-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20250214191641.756664-1-namhyung@kernel.org
Signed-off-by: Namhyung Kim <namhyung@kernel.org>