drm/modes: parse_cmdline: Explicitly memset the passed in drm_cmdline_mode struct

Instead of only setting mode->specified on false on an early exit and
leaving e.g. mode->bpp_specified and mode->refresh_specified as is,
lets be consistent and just zero out the entire passed in struct at
the top of drm_mode_parse_command_line_for_connector()

Changes in v3:
-Drop "mode->specified = false;" line instead of the "return false;" (oops)
 This crasher was reported-by: kernel test robot <lkp@intel.com>
Acked-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191118155134.30468-11-hdegoede@redhat.com

drivers/gpu/drm/drm_modes.c

@@ -1745,12 +1745,11 @@ bool drm_mode_parse_command_line_for_connector(const char *mode_option,
 	char *bpp_end_ptr = NULL, *refresh_end_ptr = NULL;
 	int i, len, ret;
 
+	memset(mode, 0, sizeof(*mode));
 	mode->panel_orientation = DRM_MODE_PANEL_ORIENTATION_UNKNOWN;
 
-	if (!mode_option) {
-		mode->specified = false;
+	if (!mode_option)
 		return false;
-	}
 
 	name = mode_option;