mesa: fix leaking ParameterValueOffset

mesa: fix leaking ParameterValueOffset

==15115== 48 bytes in 1 blocks are definitely lost in loss record 16 of 66
==15115==    at 0x4C2EC15: realloc (vg_replace_malloc.c:785)
==15115==    by 0x8602C3E: _mesa_reserve_parameter_storage (prog_parameter.c:212)
==15115==    by 0x8602D1E: _mesa_add_parameter (prog_parameter.c:252)
==15115==    by 0x86032C4: _mesa_add_sized_state_reference (prog_parameter.c:384)
==15115==    by 0x8603324: _mesa_add_state_reference (prog_parameter.c:409)

Fixes: edded12376 "mesa: rework ParameterList to allow packing"
Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>