Revert "intel/compiler: split is_partial_write() into two variants"

This reverts commit 40b3abb4d1.

It is not clear that this commit was entirely correct, and unfortunately
it was pushed by error.

CC: Jason Ekstrand <jason@jlekstrand.net>
Acked-by: Jason Ekstrand <jason@jlekstrand.net>

src/intel/compiler/brw_fs_reg_allocate.cpp

@@ -1066,7 +1066,7 @@ fs_visitor::spill_reg(unsigned spill_reg)
           * write, there should be no need for the unspill since the
           * instruction will be overwriting the whole destination in any case.
 	  */
-         if (inst->is_partial_reg_write() ||
+         if (inst->is_partial_write() ||
              (!inst->force_writemask_all && !per_channel))
             emit_unspill(ubld, spill_src, subset_spill_offset,
                          regs_written(inst));