hp-plus: fix link objects

Fix hp-plus Makefile object file:

drivers/built-in.o: In function `hpp_open':
hp-plus.c:(.text+0xaf445): undefined reference to `ei_interrupt'
hp-plus.c:(.text+0xaf4ac): undefined reference to `ei_open'
drivers/built-in.o: In function `hpp_close':
hp-plus.c:(.text+0xaf59d): undefined reference to `ei_close'
drivers/built-in.o: In function `hpp_probe1':
hp-plus.c:(.init.text+0x7314): undefined reference to `ei_poll'
drivers/built-in.o: In function `hp_plus_probe':
(.init.text+0x7407): undefined reference to `__alloc_ei_netdev'
make[1]: *** [.tmp_vmlinux1] Error 1

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>