slcan: Add missing linux/sched.h include.

slcan: Add missing linux/sched.h include.

drivers/net/can/slcan.c: In function 'slcan_open':
drivers/net/can/slcan.c:568: error: dereferencing pointer to incomplete type

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
Upstream commit:
http://git.kernel.org/?p=linux/kernel/git/davem/net-next-2.6.git;a=commitdiff;h=84b3cdc38cd2882d7ac3c2ae4b6faf5c199874e3

git-svn-id: svn://svn.berlios.de//socketcan/trunk@1224 030b6a49-0b11-0410-94ab-b0dab22257f2