drm/radeon: Clean up code in radeon_pci_shutdown()

This fixes the formatting on one comment and consolidates the
pci_get_drvdata() into the radeon_suspend_kms().

Signed-off-by: Kyle Mahlkuch <kmahlkuc@linux.vnet.ibm.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>