dma_core_wrap, idma_reg64_frontend: Minor fixes

[Vyeow]

In dma_core_wrap we encountered this error:
Error: src/systems/cva6_reg/dma_core_wrap.sv(60): 'burst_req_t' is an unknown type.
We believe that this was meant to be idma_req_t as this type was declared just before.

And in idma_reg64_frontend we encountered these warnings:

Warning: (vsim-3015) [PCDPC] - Port size (64) does not match connection size (48) for port 'next_o'. The port definition is at: src/frontends/idma_transfer_id_gen.sv(19).
File: src/frontends/register_64bit/idma_reg64_frontend.sv Line: 143

Warning: (vsim-3015) [PCDPC] - Port size (64) does not match connection size (48) for port 'completed_o'. The port definition is at: src/frontends/idma_transfer_id_gen.sv(21).
File: src/frontends/register_64bit/idma_reg64_frontend.sv Line: 143

The signals next_id, done_id are declared with length DmaAddrWidth instead of DmaRegisterWidth. We believe that this is unintentional, as the config registers are 64 bits wide.
However, note that with this fix the parameter DmaAddrWidth will not be used anywhere in the module.

[thommythomaso]

LGTM. I will remove the parameter and merge.