drivers/pcmcia: add missing pci_dev_get

pci_get_slot does a pci_dev_get, so pci_dev_put needs to be called in an
error case.

An extract of the semantic match used to find the problem is as follows:
(http://www.emn.fr/x-info/coccinelle/

)

// <smpl>
@@
type find1.T,T1,T2;
identifier find1.E;
statement find1.S;
expression x1,x2,x3;
expression find1.test;
int ret != 0;
@@

  T E;
  ...
(
* E = pci_get_slot(...);
  if (E == NULL) S
|
* if ((E = pci_get_slot(...)) == NULL)
  S
)
  ... when != pci_dev_put(...,(T1)E,...)
      when != if (E != NULL) { ... pci_dev_put(...,(T1)E,...); ...}
      when != x1 = (T1)E
      when != E = x3;
      when any
  if (test) {
    ... when != pci_dev_put(...,(T2)E,...)
        when != if (E != NULL) { ... pci_dev_put(...,(T2)E,...); ...}
        when != x2 = (T2)E
(
*   return;
|
*   return ret;
)
  }
// </smpl>

Signed-off-by: Julia Lawall <julia@diku.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>