bpf: fix the return value of push_stack

bpf: fix the return value of push_stack

In [1] Eduard mentioned that on push_stack failure verifier code
should return -ENOMEM instead of -EFAULT. After checking with the
other call sites I've found that code randomly returns either -ENOMEM
or -EFAULT. This patch unifies the return values for the push_stack
(and similar push_async_cb) functions such that error codes are
always assigned properly.

  [1] https://lore.kernel.org/bpf/20250615085943.3871208-1-a.s.protopopov@gmail.com

Signed-off-by: Anton Protopopov <a.s.protopopov@gmail.com>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20251019202145.3944697-2-a.s.protopopov@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>