bpf: enforce precision of R0 on program/async callback return

Given we enforce a valid range for program and async callback return
value, we must mark R0 as precise to avoid incorrect state pruning.

Fixes: b5dc0163 ("bpf: precise scalar_value tracking")
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20231202175705.885270-9-andrii@kernel.org


Signed-off-by: Alexei Starovoitov <ast@kernel.org>