PCMCIA: fix sa1111 oops on remove

The sa1111 socket driver oopses when removed:

Unable to handle kernel NULL pointer dereference at virtual address 000003b0
pgd = c1b40000
[000003b0] *pgd=00000000
Internal error: Oops: 41b43005 [#1]
Modules linked in:
CPU: 0    Not tainted  (3.3.0-rc1+ #744)
PC is at pcmcia_remove+0x3c/0x60
LR is at pcmcia_remove+0x34/0x60

This is because we try to dereference a NULL 's' to obtain the next
pointer.  Fix this.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>