wifi: iwlwifi: simplify iwl_poll_bits_mask return value

Update iwl_poll_bits_mask to return 0 on success or an error code.
Remove timing information from the return value, as it is unused.

Signed-off-by: Itamar Shalev <itamar.shalev@intel.com>
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://patch.msgid.link/20250709230308.f77b9f484a78.Iae8ef99a94e25c23044e2c36244cda2b55328447@changeid