[PATCH] libertas link error due to gcc `smartness'

Some versions of gcc replace strstr() calls with a single-character `needle'
parameter by strchr() behind our back. This causes a link error if strchr() is
defined as an inline function in <asm/string.h> (e.g. on m68k):

| drivers/built-in.o: In function `libertas_parse_chan':
| linux/drivers/net/wireless/libertas/debugfs.c:209: undefined reference to `strchr'
| drivers/built-in.o: In function `libertas_parse_ssid':
| linux/drivers/net/wireless/libertas/debugfs.c:260: undefined reference to `strchr'

Avoid this by explicitly calling strchr() instead.

Also include <linux/string.h>, because this file calls lots of str*() routines.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-By: Holger Schurig <hs4233@mail.mn-solutions.de>
Acked-By: Dan Williams <dcbw@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>