Fix regwidth & accesswidth on buffer triggers when trigger is a RegNode

[apstrike]

Currently, in get_trigger in the ReadBuffering and WriteBuffering classes when a read/write buffer trigger is of type RegNode, the RegNode that will be stored is being used to determine the regwidth and accesswidth of the trigger. This is being used to determine how to access the trigger, this is incorrect when the trigger is not the node being stored. Instead, the trigger's properties should be used to determine how to access it.

For example, the code snippet (assuming default accesswidth=32; default regwidth=32):

reg {
    field {} trigger_reg_field[32];
} trigger_reg;

reg {
    sw =r; hw = w;
    regwidth = 128;
    field reg_field[128];
} my_reg;

my_reg->buffer_reads = true;
my_reg->rbuffer_trigger = trigger_reg;

Would generate code that look like:

// note: decoded_reg_strb.trigger_reg is of type `logic` not `logic [0:0]`
always_ff @(posedge clk) begin
    if (decoded_reg_strb.trigger_reg[0] && !decoded_req_is_wr) begin
        rbuf.my_reg.reg_field[127:0] <= hwif_in.my_reg.reg_field[127:0];
   end
end

Here, the access to decoded_reg_strb.trigger_reg[0] would be illegal (at least Questa doesn't permit it), but it would be generated as so because my_reg.accesswidth < my_reg.regwidth.
In truth it's trigger_reg.accesswidth and trigger_reg.regwidth that should be compared to get the correct access to the trigger.

[amykyta3]

Ha! This definitely looks like a copy/paste mistake on my part.
Thanks for figuring it out and fixing it!