wifi: iwlwifi: mld: tests: simplify le32 bitfield handling

We can use le32_encode_bits() instead of cpu_to_le32()
combined with FIELD_PREP().

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://patch.msgid.link/20250423091408.9155a412dcc7.I8330ca413d6bdf953e79361ac50939176bcc4e6e@changeid


Signed-off-by: Johannes Berg <johannes.berg@intel.com>