i965/fs: Recalculate live intervals in calculate_register_pressure().

Otherwise calling dump_instructions() after declaring a new fs_reg would
segfault when calculate_register_pressure()'s loop over reg walked off
the end of the virtual_grf_start[] array that calculate_live_intervals()
would have reallocated for you, if it had known there was a new
register.

src/mesa/drivers/dri/i965/brw_fs.cpp

@@ -3294,6 +3294,7 @@ fs_visitor::assign_binding_table_offsets()
 void
 fs_visitor::calculate_register_pressure()
 {
+   invalidate_live_intervals();
    calculate_live_intervals();
 
    int num_instructions = 0;