staging: comedi: amplc_pc263: fix possible NULL deref during detach
staging: comedi: amplc_pc263: fix possible NULL deref during detach

`pc263_detach()` is called by the comedi core to clean up if either
`pc263_attach()` or `pc263_attach_pci()` returns an error.  It sets
`thisboard` to the return value of `comedi_board(dev)` and assumes it is
non-null.  This is a valid assumption if `pc263_attach()` fails, but not
if `pc263_attach_pci()` fails, leading to a possible NULL pointer
dereference.

Check `thisboard` at the top of `pc263_detach()` and return early if it
is `NULL`.  This is okay because no other resources need cleaning up in
this case.

Cc: <4fbacc2fa0ffdbb11bf1ad6925b886ebd08dd15f@vger.kernel.org> # 3.6.x
Signed-off-by: Ian Abbott <9e6ba6483b6a3e14d61f7c987e72ecb5b46122d6@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <4645f7897fd33786a2ee1264d590b3c400559d85@linuxfoundation.org>

KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas