linuxkpi: Remove incorrect + 1 from HWEIGHT* macros

Fixes: 4cc8a9da491d ("LinuxKPI: add HWEIGHT32()")
Reviewed by: bz
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D51010

(cherry picked from commit cdbff1b2999660b31b2de076d04670722a555ed2)