[netdrvr] Fix 8390 build breakage

From: tony@bakeyournoodle.com (Tony Breeds)

The commit 3f8cb098
(drivers/net/lib8390: fix warning, trim trailing whitespace) removed
ei_local from ei_tx_err() and ei_rx_overrun() resulting in the following
build errors on m68k and sh:

Using /scratch1/tony/next as source for kernel
GEN     /scratch1/tony/next_out/Makefile
CHK     include/linux/version.h
CHK     include/linux/utsrelease.h
CALL    /scratch1/tony/next/scripts/checksyscalls.sh
CHK     include/linux/compile.h
CC [M]  drivers/net/zorro8390.o
In file included from /scratch1/tony/next/drivers/net/zorro8390.c:47:
drivers/net/lib8390.c: In function 'ei_tx_err':
drivers/net/lib8390.c:556: error: 'ei_local' undeclared (first use in this function)
drivers/net/lib8390.c:556: error: (Each undeclared identifier is reported only once
drivers/net/lib8390.c:556: error: for each function it appears in.)
drivers/net/lib8390.c: In function 'ei_rx_overrun':
drivers/net/lib8390.c:823: error: 'ei_local' undeclared (first use in this function)
make[3]: *** [drivers/net/zorro8390.o] Error 1
make[2]: *** [drivers/net] Error 2
make[1]: *** [drivers] Error 2
make: *** [sub-make] Error 2

The problem is that ei_inb_p() is using various #defines (from
drivers/net/8390.h) that use EI_SHIFT, which in some drivers on some
architectures use ei_local.  Tag ei_local as "__maybe_unused" to keep it
around and keep the warnings the original commit is trying to silence
... silenced.

Signed-off-by: Tony Breeds <tony@bakeyournoodle.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>