pcmcia: Fix a NULL pointer dereference in __iodyn_find_io_region()

In __iodyn_find_io_region(), pcmcia_make_resource() is assigned to
res and used in pci_bus_alloc_resource(). There is a dereference of res
in pci_bus_alloc_resource(), which could lead to a NULL pointer
dereference on failure of pcmcia_make_resource().

Fix this bug by adding a check of res.

Cc: [e-mail]
Fixes: 49b1153adfe1 ("pcmcia: move all pcmcia_resource_ops providers into one module")
Signed-off-by: Ma Ke <[e-mail]>
Signed-off-by: Dominik Brodowski <[e-mail]>

drivers/pcmcia/rsrc_iodyn.c

···
 	unsigned long min = base;
 	int ret;
 
+	if (!res)
+		return NULL;
+
 	data.mask = align - 1;
 	data.offset = base & data.mask;