drm/cmdline-parser: Merge negative tests

Negative tests can be expressed as a single parameterized test case,
which highlights that we're following the same test logic (passing
invalid cmdline and expecting drm_mode_parse_command_line_for_connector
to fail), which improves readability.

v2: s/negative/invalid to be consistent with other testcases in DRM

Signed-off-by: Michał Winiarski <michal.winiarski@intel.com>
Reviewed-by: Maíra Canal <mairacanal@riseup.net>
Signed-off-by: Maíra Canal <mairacanal@riseup.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20220817211236.252091-1-michal.winiarski@intel.com