Fix: radeon_platform_probed return ture while kernel driver is amdgpu

For machines have two AMD graphic cards, and the first graphic card's kernel driver is radeon, the second graphic card belongs SI/CIK chipset which could use both radeon and amdgpu for kernel driver. When using kernel command line "radeon.si_support=0 amdgpu.si_support=1" to switch the second card's kernel driver to be amdgpu, as xserver probing DDX driver for the second graphic card, radeon_platform_probe will returned ture while kernel driver is amdgpu, that will cause xserver terminated with error In the following process of AddScreen/ScreenInit.

This can be fixed by adding driver name compare to radeon_platform_probe.

This fixes #181

Signed-off-by: hongao hongao@uniontech.com