drm: bridge/dw_hdmi: remove mhsyncpolarity/mvsyncpolarity/minterlaced

Remove the struct hdmi_vmode mhsyncpolarity/mvsyncpolarity/minterlaced
members, which are only used within a single function.  We can directly
reference the appropriate mode->flags instead.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>