mISDN: DSP scheduling fix (version 2)

dsp_spl_jiffies need to be the same datatype as jiffies (which is ulong).
If not, on 64 bit systems it will fallback to schedule the DSP every jiffie
tic as soon jiffies become > 2^32.

Signed-off-by: Karsten Keil <kkeil@linux-pingi.de>
Signed-off-by: David S. Miller <davem@davemloft.net>