drm/amdgpu: fix off by one in amdgpu_gfx_kiq_acquire()

This post-op should be a pre-op so that we do not pass -1 as the bit
number to test_bit().  The current code will loop downwards from 63 to
-1.  After changing to a pre-op, it loops from 63 to 0.

Fixes: 71c3750 ("drm/amdgpu/gfx: move more common KIQ code to amdgpu_gfx.c")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -266,7 +266,7 @@ static int amdgpu_gfx_kiq_acquire(struct amdgpu_device *adev,
 		    * adev->gfx.mec.num_pipe_per_mec
 		    * adev->gfx.mec.num_queue_per_pipe;
 
-	while (queue_bit-- >= 0) {
+	while (--queue_bit >= 0) {
 		if (test_bit(queue_bit, adev->gfx.mec.queue_bitmap))
 			continue;