hisax: remove bad udelay call to fix build error on ARM

The hisax ISDN driver fails to build on ARM with CONFIG_HISAX_ELSA:

| drivers/built-in.o: In function `modem_set_dial':
| drivers/isdn/hisax/elsa_ser.c:535: undefined reference to `__bad_udelay'
| drivers/isdn/hisax/elsa_ser.c:544: undefined reference to `__bad_udelay'
| drivers/built-in.o: In function `modem_set_init':
| drivers/isdn/hisax/elsa_ser.c:486: undefined reference to `__bad_udelay'
| [...]

According to the comment in arch/arm/include/asm/delay.h, __bad_udelay
is specifically designed on ARM to produce a build failure when udelay
is called with a value > 2000.

Signed-off-by: Martin Michlmayr <tbm@cyrius.com>
Signed-off-by: David S. Miller <davem@davemloft.net>