RELENG_5 build broken with BKTR_USE_FREEBSD_SMBUS and BKTR_NEW_MSP34XX_DRIVER enabled

In trying to build a kernel with bktr support, I'm using both
BKTR_USE_FREEBSD_SMBUS and BKTR_NEW_MSP34XX_DRIVER.  This is what I see on a
compile:

    cc -c -O -pipe -march=pentium4 -Wall -Wredundant-decls -Wnested-externs \
      -Wstrict-prototypes  -Wmissing-prototypes -Wpointer-arith -Winline \
      -Wcast-qual  -fformat-extensions -std=c99  -nostdinc -I-  -I. \
      -I/usr/src/sys -I/usr/src/sys/contrib/dev/acpica \
      -I/usr/src/sys/contrib/altq -I/usr/src/sys/contrib/ipfilter \
      -I/usr/src/sys/contrib/pf -I/usr/src/sys/contrib/dev/ath \
      -I/usr/src/sys/contrib/dev/ath/freebsd \
      -I/usr/src/sys/contrib/ngatm -D_KERNEL -include opt_global.h \
      -fno-common -finline-limit=8000 --param inline-unit-growth=100 \
      --param large-function-growth=1000  -mno-align-long-strings \
      -mpreferred-stack-boundary=2 -ffreestanding -Werror  \
      /usr/src/sys/dev/bktr/msp34xx.c
    In file included from /usr/src/sys/dev/bktr/msp34xx.c:92:
    /usr/src/sys/dev/bktr/bktr_reg.h:451: error: syntax error before "device_t"
    *** Error code 1

    Stop in /usr/obj/usr/src/sys/dementia.
    *** Error code 1

    Stop in /usr/src.
    *** Error code 1

    Stop in /usr/src.

Removing either option fixes the build.  The only thing in NOTES that might
address this is the note saying bktr has been ported to the new I2C
framework.  Is this an obvious don't-do-that?