drm/amdkfd: Fix signal_eviction_fence() bool return value

signal_eviction_fence() is declared to return bool, but returns -EINVAL
when no eviction fence is present.  This makes the "no fence" or "the
NULL-fence" path evaluate to true and triggers a Smatch warning.

v2: Return true instead to explicitly indicate that there is no eviction
fence to signal and that eviction is already complete. This matches the
existing caller logic where a NULL fence means "nothing to do" and
allows restore handling to proceed normally. (Christian)

Fixes the below:
drivers/gpu/drm/amd/amdgpu/../amdkfd/kfd_process.c:2099 signal_eviction_fence()
warn: '(-22)' is not bool

drivers/gpu/drm/amd/amdgpu/../amdkfd/kfd_process.c
    2090 static bool signal_eviction_fence(struct kfd_process *p)
                ^^^^

    2091 {
    2092         struct dma_fence *ef;
    2093         bool ret;
    2094
    2095         rcu_read_lock();
    2096         ef = dma_fence_get_rcu_safe(&p->ef);
    2097         rcu_read_unlock();
    2098         if (!ef)
--> 2099                 return -EINVAL;

		This should be either true or false.
		Probably true because presumably
		it has been tested?

    2100
    2101         ret = dma_fence_check_and_signal(ef);
    2102         dma_fence_put(ef);
    2103
    2104         return ret;
    2105 }

Fixes: 37865e02e6 ("drm/amdkfd: Fix eviction fence handling")
Reported by: Dan Carpenter <dan.carpenter@linaro.org>
Cc: Philip Yang <Philip.Yang@amd.com>
Cc: Gang BA <Gang.Ba@amd.com>
Cc: Felix Kuehling <felix.kuehling@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -2096,7 +2096,7 @@ static int signal_eviction_fence(struct kfd_process *p)
 	ef = dma_fence_get_rcu_safe(&p->ef);
 	rcu_read_unlock();
 	if (!ef)
-		return -EINVAL;
+		return true;
 
 	ret = dma_fence_signal(ef);
 	dma_fence_put(ef);