0.5.2

vendor._gowin: fix clock name quotes for Gowin IDE

Gowin IDE seems unhappy with quotes in clock signal names. For instance,
with the following SDC:

create_clock -name "clk50_0__io" -period 20.0 [get_ports
    {clk50_0__io}]

Gowin IDE will complain with the following error message:

ERROR  (TA2000) : "top.sdc":2 | 'syntax error' near token '-period'

Changing quotes with curly braces fixes the issue.