perf lock: Fix return code for functions in __cmd_contention

perf lock: Fix return code for functions in __cmd_contention

perf lock contention returns zero exit value even if the lock contention
BPF setup failed.

  # ./perf lock con -b true
  libbpf: kernel BTF is missing at '/sys/kernel/btf/vmlinux', was CONFIG_DEBUG_INFO_BTF enabled?
  libbpf: failed to find '.BTF' ELF section in /lib/modules/6.13.0-rc3+/build/vmlinux
  libbpf: failed to find valid kernel BTF
  libbpf: kernel BTF is missing at '/sys/kernel/btf/vmlinux', was CONFIG_DEBUG_INFO_BTF enabled?
  libbpf: failed to find '.BTF' ELF section in /lib/modules/6.13.0-rc3+/build/vmlinux
  libbpf: failed to find valid kernel BTF
  libbpf: Error loading vmlinux BTF: -ESRCH
  libbpf: failed to load object 'lock_contention_bpf'
  libbpf: failed to load BPF skeleton 'lock_contention_bpf': -ESRCH
  Failed to load lock-contention BPF skeleton
  lock contention BPF setup failed
  # echo $?
   0

Fix this by saving the return code for lock_contention_prepare
so that command exits with proper return code. Similarly set the
return code properly for two other functions in builtin-lock, namely
setup_output_field() and select_key().

Signed-off-by: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20250110093730.93610-1-atrajeev@linux.vnet.ibm.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>