Staging: comedi: drivers: Delete NULL check before pci_dev_put

The function pci_dev_put checks whether its argument is NULL and returns
immediately. Therefore, NULL test before the call if not needed.
Found using coccinelle:
@@
expression x;
@@

- if(x)
- pci_dev_put(x);
+ pci_dev_put(x);

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>