[SPARC64]: Fix make headers_install

A minor typo in the include/asm-sparc64/Kbuild file prevents the make
headers_install from building a useful tree of kernel headers for
sparc64.
Signed-off-by: NDavid Woodhouse <dwmw2@infradead.org>
Signed-off-by: NTom "spot" Callaway <tcallawa@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/asm-sparc64/Kbuild

@@ -4,7 +4,7 @@ ALTARCH := sparc
 ARCHDEF := defined __sparc__ && defined __arch64__
 ALTARCHDEF := defined __sparc__ && !defined __arch64__
 
-unifdef-y := fbio.h perfctr.h
+unifdef-y += fbio.h perfctr.h
 header-y += apb.h asi.h bbc.h bpp.h display7seg.h envctrl.h floppy.h	\
 	ipc.h kdebug.h mostek.h openprom.h openpromio.h parport.h	\
 	pconf.h psrcompat.h pstate.h reg.h uctx.h utrap.h watchdog.h