etnaviv: remove variable from global namespace

Found out by accident this was clashing with another driver.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Reviewed-by: Kristian H. Kristensen <hoegsberg@google.com>
Cc: <mesa-stable@lists.freedesktop.org>
(cherry picked from commit 701e0ac0)