drm: lcdif: Drop unnecessary NULL pointer check on lcdif->bridge

A valid bridge is already found in lcdif_attach_bridge() and set
to lcdif->bridge, so lcdif->bridge cannot be a NULL pointer. Drop
the unnecessary NULL pointer check in KMS stage.

Tested-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Reviewed-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Signed-off-by: Liu Ying <victor.liu@nxp.com>
Reviewed-by: Marek Vasut <marex@denx.de>
Signed-off-by: Marek Vasut <marex@denx.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20230510092450.4024730-3-victor.liu@nxp.com