CVE-2026-74442: drm/vmwgfx: avoid destroy_workqueue(NULL) on vkms init failure

In the Linux kernel, the following vulnerability has been resolved:

drm/vmwgfx: avoid destroyworkqueue(NULL) on vkms init failure

Two paths through vmwvkmsinit() can leave vmw->crcworkq NULL while still leaving the rest of the driver in a state that calls vmwvkmscleanup() at module unload:

1. vmwhostgetguestinfo(GUESTINFOVBLANK, ...) failing or returning an oversized buffer -- the common case on hosts without a VBLANK guestinfo entry -- early-returned before the workqueue allocation. 2. allocorderedworkqueue() returning NULL on memory pressure.

vmwvkmscleanup() then calls destroyworkqueue(NULL), which dereferences wq->name and panics.

Fix the first case by removing the early return: vmw->vkmsenabled is already false on the rpci-failure path so no work will ever be queued, and allocating the workqueue unconditionally keeps the control flow simple. Fix the second case by guarding the cleanup with a NULL check, since allocorderedworkqueue() can still fail under low memory.