drm/i915/pmu: Check if pmu is closed before stopping event

drm/i915/pmu: Check if pmu is closed before stopping event

When the driver unbinds, pmu is unregistered and i915->uabi_engines is
set to RB_ROOT. Due to this, when i915 PMU tries to stop the engine
events, it issues a warn_on because engine lookup fails.

All perf hooks are taking care of this using a pmu->closed flag that is
set when PMU unregisters. The stop event seems to have been left out.

Check for pmu->closed in pmu_event_stop as well.

Based on discussion here -
https://patchwork.freedesktop.org/patch/492079/?series=105790&rev=2

v2: s/is/if/ in commit title
v3: Add fixes tag and cc stable

Cc: <stable@vger.kernel.org> # v5.11+
Fixes: b00bccb3f0bb ("drm/i915/pmu: Handle PCI unbind")
Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231020152441.3764850-1-umesh.nerlige.ramappa@intel.com