There's two files in the sys tree named inflate.c, in addition
to it being a common name elsewhere. Rename the old kzip one
to subr_inflate.c.

This actually fixes the build issues on sparc64 that my inclusion of
.PATH ${SYSDIR}/kern created in r336244, so also revert the broken
workaround I committed in r336249.

This slipped passed me because apparently, I never did a clean build.