staging: slicoss: fix a null deref when pci_alloc_consistent fail

we are dereferencing the pshmem , and the pci_alloc_consistent can fail
returning null,

do a memcpy if we have a valid pshmem

Signed-off-by: Devendra Naga <devendra.aaru@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>