drm: renesas: rz-du: mipi_dsi: Add min check for VCLK range

drm: renesas: rz-du: mipi_dsi: Add min check for VCLK range

The VCLK range for Renesas RZ/G2L SoC is 5.803 MHz to 148.5 MHz. Add a
minimum clock check in the mode_valid callback to ensure that the clock
value does not fall below the valid range.

Co-developed-by: Fabrizio Castro <fabrizio.castro.jz@renesas.com>
Signed-off-by: Fabrizio Castro <fabrizio.castro.jz@renesas.com>
Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Link: https://lore.kernel.org/r/20250609225630.502888-2-prabhakar.mahadev-lad.rj@bp.renesas.com