i965: Use C99 struct initializers in brw_bufmgr.c.

i965: Use C99 struct initializers in brw_bufmgr.c.

This is cleaner than using a non-standard memclear macro (which does a
memset to 0) and then initializing fields after the fact.  We move the
declarations to where we initialized the fields.  While we're at it, we
move the declaration of 'ret' that goes with the ioctl, eliminating the
declaration section altogether.

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>