drm/amd: Make SDMA firmware load failures less noisy.

When firmware is missing we get failures at every step.
```
[    3.855086] amdgpu 0000:04:00.0: Direct firmware load for amdgpu/green_sardine_sdma.bin failed with error -2
[    3.855087] [drm:amdgpu_sdma_init_microcode [amdgpu]] *ERROR* SDMA: Failed to init firmware "amdgpu/green_sardine_sdma.bin"
[    3.855398] [drm:sdma_v4_0_early_init [amdgpu]] *ERROR* Failed to load sdma firmware!
```
Realistically we don't need all of these, a user can tell from the first one
that request_firmware emitted what happened. Drop the others.

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>