/swr: Fix multi-context sync fence deadlock.
Various recreation scenarios lead to API thread getting stuck in
swr_fence_finish(). This is a multi-context issue, whereby one context
overwrites the fence read-value with a previous sync's lesser value.
The fence sync value is supposed to be always
Various recreation scenarios lead to API thread getting stuck in
swr_fence_finish(). This is a multi-context issue, whereby one context
overwrites the fence read-value with a previous sync's lesser value.
The fence sync value is supposed to be always increasing.
In swr_fence_cb(), only update
