USB: goku_udc: remove potential null dereference

"dev" is always null here.  In the end it's only used to get the
pci_name() of "pdev" which is redundant information and so I
removed it.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>