drm/i915: Call i915_globals_exit() if pci_register_device() fails

In the unlikely event that pci_register_device() fails, we were tearing
down our PMU setup but not globals.  This leaves a bunch of memory slabs
lying around.

Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
Fixes: 32eb6bcf ("drm/i915: Make request allocation caches global")
[danvet: Fix conflicts against removal of the globals_flush
infrastructure.]
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210721152358.2893314-3-jason@jlekstrand.net