kernel build failure, es1888.c is listed in makefile

Hi,

I got kernel build failure today when I tried to upgrade RELENG_6 to 
CURRENT.
...
rm -f .depend
mkdep -f .depend -a   -nostdinc -D_KERNEL -DKLD_MODULE -I- 
-DHAVE_KERNEL_OPTION_HEADERS -I. -I_at_ -I_at_/contrib/altq 
-I/usr/obj/usr/src/sys/GW 
/usr/src/sys/modules/sound/driver/es137x/../../../../dev/sound/pci/es137x.c
===> sound/driver/ess (depend)
_at_ -> /usr/src/sys
machine -> /usr/src/sys/i386/include
awk -f _at_/tools/makeobjops.awk _at_/kern/device_if.m -h
awk -f _at_/tools/makeobjops.awk _at_/kern/bus_if.m -h
awk -f _at_/tools/makeobjops.awk _at_/isa/isa_if.m -h
awk -f _at_/tools/makeobjops.awk _at_/dev/pci/pci_if.m -h
make: don't know how to make es1888.c. Stop
*** Error code 2

Stop in /usr/src/sys/modules/sound/driver.
*** Error code 1

I checked the makefile and es1888.c is listed in makefile but file 
itself is missing.
Either makefile should be fixed or es1888.c file added in appropriate place.

thanks,

Ganbold