usb-dbg: remove is_method_error call

An `is_method_error` is not appropriate after an sdbus `call` since
`call` will always throw an exception.  Remove the pointless call
and instead catch the exception.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I8f4f1f3b257e7a0e8d54eb96273504455d611857
1 file changed