i965/cfg: Initialize bblock_t::cycle_count.

schedule_instructions(bblock_t *) isn't called on blocks with a single
instruction, and since it is the only thing that set cycle_count,
cycle_count would be uninitialized.

A non-empty block with bblock_t::cycle_count == 0 is arguably a bug.
That'll be fixed in the next commit.

Reviewed-by: Francisco Jerez <currojerez@riseup.net>

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

@@ -51,7 +51,7 @@ link(void *mem_ctx, bblock_t *block)
 }
 
 bblock_t::bblock_t(cfg_t *cfg) :
-   cfg(cfg), idom(NULL), start_ip(0), end_ip(0), num(0)
+   cfg(cfg), idom(NULL), start_ip(0), end_ip(0), num(0), cycle_count(0)
 {
    instructions.make_empty();
    parents.make_empty();