LinuxKPI: fix bug in le32p_replace_bits()

Fix a bug that slipped in in 90707c4e44de03ea36be183ef2226601c66169cb
using the correct field in le32p_replace_bits().

MFC after: 3 days
Reviewed by: hselasky
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D31352