i965: Re-index SSA definitions before printing NIR code.

i965: Re-index SSA definitions before printing NIR code.

This makes the SSA definitions use sequential numbers (0, 1, 2, ...)
instead of seemingly random ones.  There's not much point normally,
but it makes debug output much easier to read.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Reviewed-by: Connor Abbott <cwabbott0@gmail.com>