drm/amdgpu: remove set but not used variable 'pipe'

Fixes gcc '-Wunused-but-set-variable' warning:

rivers/gpu/drm/amd/amdgpu/amdgpu_gfx.c: In function
‘amdgpu_gfx_graphics_queue_acquire’:
drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.c:234:16: warning:
variable ‘pipe’ set but not used [-Wunused-but-set-variable]

It is never used, so can be removed.
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: yu kuai <yukuai3@huawei.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -232,12 +232,10 @@ void amdgpu_gfx_compute_queue_acquire(struct amdgpu_device *adev)
 
 void amdgpu_gfx_graphics_queue_acquire(struct amdgpu_device *adev)
 {
-	int i, queue, pipe, me;
+	int i, queue, me;
 
 	for (i = 0; i < AMDGPU_MAX_GFX_QUEUES; ++i) {
 		queue = i % adev->gfx.me.num_queue_per_pipe;
-		pipe = (i / adev->gfx.me.num_queue_per_pipe)
-			% adev->gfx.me.num_pipe_per_me;
 		me = (i / adev->gfx.me.num_queue_per_pipe)
 		      / adev->gfx.me.num_pipe_per_me;