mei: rename struct pci_dev *mei_device to mei_pdev

1. rename mei_device variable to mei_pdev to remove
confusion with type 'struct mei_device'
2. mei_pdev no longer need to be gloabal so make it static
 and remove the declaration from the header file

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>