mdis_kernel: Decrement the pci_dev reference count after use pci_get_slot()
requested to merge 391-men_oss-when-pci_get_slot-is-called-the-reference-count-of-this-pci-device-is-increased-and into mad-dev
The function pci_get_slot() increments the internal ref counter of pci_dev so, we need to call to pci_dev_put() to decrement such ref counter once we have finished. Not using this function can lead to a kernel crash.
Closes #391