commit e79d5c08 upstream.

Make sure we are not the root device before attempting to
read the pcie bridge registers to check the pcie gen speeed.

Fixes a crash when the device is passed through to a VM.
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>