perf/core: Simplify perf_event_alloc()

Using the previous simplifications, transition perf_event_alloc() to
the cleanup way of things -- reducing error path magic.

[ mingo: Ported it to recent kernels. ]

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Ravi Bangoria <ravi.bangoria@amd.com>
Link: https://lore.kernel.org/r/20241104135518.410755241@infradead.org