nir: free dead_ctx in case of no progress

nir: free dead_ctx in case of no progress

Fixes a leak:

  ==7576== 320 (48 direct, 272 indirect) bytes in 1 blocks are definitely lost in loss record 26 of 26
  ==7576==    at 0x4C2EE3B: malloc (vg_replace_malloc.c:309)
  ==7576==    by 0x53EF0E4: ralloc_size (ralloc.c:119)
  ==7576==    by 0x53EF0C2: ralloc_context (ralloc.c:113)
  ==7576==    by 0x5471F64: nir_split_per_member_structs (nir_split_per_member_structs.c:176)
  ==7576==    by 0x51288CF: anv_shader_compile_to_nir (anv_pipeline.c:216)

Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>