can: c_can_pci: enable PCI bus master only for MSI

Coverity complains that c_can_pci_probe() calls pci_enable_msi() without
checking the result:

CID 712278 (#1 of 1): Unchecked return value (CHECKED_RETURN) 3. check_return:
Calling pci_enable_msi_block without checking return value (as is done
elsewhere 88 out of 105 times).
 88        pci_enable_msi(pdev);

This is CID 712278.

Signed-off-by: Wolfgang Grandegger <wg@grandegger.com>
Reported-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>