Fix DapSetLogLevel when passing space after the level

[RoadRoller01]

if you passed a space after the level it should just work you did not add any letters and its not a script.
In example if you typed:
“DapSetLogLevel DEBUG “
it will not work,
So I trimmed the function args, I also replaced unpack(opts.fargs) with opts.args because it will return the same result with less code

Note:
opts.fargs is table of the function args.
unpack(table) convert table to string.
opts.args is args as string.
reference: https://neovim.io/doc/user/api.html#nvim_create_user_command()

[mfussenegger]

Thanks