drm/amdkfd: set "r = 0" explicitly before goto

To silence the following Smatch static checker warning:

drivers/gpu/drm/amd/amdgpu/../amdkfd/kfd_svm.c:2615
svm_range_restore_pages()
	warn: missing error code here? 'get_task_mm()' failed. 'r' = '0'
Signed-off-by: Philip Yang <Philip.Yang@amd.com>
Suggested-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdkfd/kfd_svm.c

@@ -2603,6 +2603,7 @@ svm_range_restore_pages(struct amdgpu_device *adev, unsigned int pasid,
 
 	if (atomic_read(&svms->drain_pagefaults)) {
 		pr_debug("draining retry fault, drop fault 0x%llx\n", addr);
+		r = 0;
 		goto out;
 	}
 
@@ -2612,6 +2613,7 @@ svm_range_restore_pages(struct amdgpu_device *adev, unsigned int pasid,
 	mm = get_task_mm(p->lead_thread);
 	if (!mm) {
 		pr_debug("svms 0x%p failed to get mm\n", svms);
+		r = 0;
 		goto out;
 	}
 
@@ -2649,6 +2651,7 @@ svm_range_restore_pages(struct amdgpu_device *adev, unsigned int pasid,
 
 	if (svm_range_skip_recover(prange)) {
 		amdgpu_gmc_filter_faults_remove(adev, addr, pasid);
+		r = 0;
 		goto out_unlock_range;
 	}
 
@@ -2657,6 +2660,7 @@ svm_range_restore_pages(struct amdgpu_device *adev, unsigned int pasid,
 	if (timestamp < AMDGPU_SVM_RANGE_RETRY_FAULT_PENDING) {
 		pr_debug("svms 0x%p [0x%lx %lx] already restored\n",
 			 svms, prange->start, prange->last);
+		r = 0;
 		goto out_unlock_range;
 	}