drm/amdgpu: Remove unneeded variable 'ret' in navi10_ih.c

Fixes coccicheck warning:

drivers/gpu/drm/amd/amdgpu/navi10_ih.c:113:5-8: Unneeded variable: "ret". Return "0" on line 182

Reported-by: Hulk Robot <[e-mail]>
Signed-off-by: Ma Feng <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/amd/amdgpu/navi10_ih.c

···
 static int navi10_ih_irq_init(struct amdgpu_device *adev)
 {
 	struct amdgpu_ih_ring *ih = &adev->irq.ih;
-	int ret = 0;
 	u32 ih_rb_cntl, ih_doorbell_rtpr, ih_chicken;
 	u32 tmp;
 
···
 	/* enable interrupts */
 	navi10_ih_enable_interrupts(adev);
 
-	return ret;
+	return 0;
 }
 
 /**