Global devargs syntax is used as device iteration filter like
"class=vdpa", a devargs without bus args is valid from parsing
perspective.
This patch makes bus args optional.
Fixes: d2a66ad79480 ("bus: add device arguments name parsing")
Signed-off-by: Xueming Li <xuemingl@nvidia.com>
Reviewed-by: Gaetan Rivet <grive@u256.net>
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