i915: Don't call _mesa_meta_glsl_Clear() on gen2

i915: Don't call _mesa_meta_glsl_Clear() on gen2

Gen2 doesn't have fragment shaders so we shouldn't be calling
_mesa_meta_glsl_Clear() on gen2. Restore the appropriate
ARB_fragment_shader check to the clear path which was lost in:

 commit 94f22fbe787214580a1a13a774114d2650c166cb
 Author: Tapani Pälli <tapani.palli@intel.com>
 Date:   Wed Aug 8 20:46:45 2012 +0300

    intel: use _mesa_meta_Clear with OpenGL ES 1.1 v2

v2: Fix spelling in commit message

Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>