i965/nir: memleak during deserialization

Member nir of gl_program may be created without context. So the object is has to be freed manually. Issue observed with piglit-test:

glsl-novertexdata -auto -fbo

Seems leak was happening in case:

1. caching of shaders is enabled
2. cache of shader wasn't generated previously or some error reading of it occurred

CC: Jordan Justen jordan.l.justen@intel.com Fixes: 1777c23a (i965: Add brw_program_deserialize_driver_blob)

Signed-off-by: Sergii Romantsov sergii.romantsov@globallogic.com