[fpv/tlul] syntax error fix
[fpv/tlul] syntax error fix

FPV gives error for this syntax:
` ../src/lowrisc_tlul_headers_0.1/rtl/tlul_pkg.sv(49): an enum variable
may only be assigned the same enum typed variable or one of its values`
DV also throws warning:
`file: ../src/lowrisc_tlul_headers_0.1/rtl/tlul_pkg.sv
    default: '0
              |
xmvlog: *W,ENUMERR (../src/lowrisc_tlul_headers_0.1/rtl/tlul_pkg.sv,48|14): This assignment is a violation of SystemVerilog strong typing rules for enumeration datatypes.
`
Please feel free to let me know if there is other better ways to fix it.

Signed-off-by: Cindy Chen <399ad771a111eac8923348b1e2af093034e5d4f1@google.com>

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