i965: Don't free the intel_context structure when intelCreateContext fails.

i965: Don't free the intel_context structure when intelCreateContext fails.

intelDestroyContext will eventually be called, and it will clean things
up.  The call to brwInitVtbl is moved earlier so that
intelDestroyContext can call the device-specific destructor.  This also
makes the code look more like the i915 code.

NOTE: This is a candidate for the 9.0 branch.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=54301