drm/rockchip: dsi: Remove the unused function dsi_update_bits()

The function dsi_update_bits() is defined in the dw-mipi-dsi-rockchip.c
file, but not called elsewhere, so delete this unused function.

drivers/gpu/drm/rockchip/dw-mipi-dsi-rockchip.c:367:20: warning: unused function 'dsi_update_bits'.

https://bugzilla.openanolis.cn/show_bug.cgi?id=2414



Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20221017084330.94117-1-jiapeng.chong@linux.alibaba.com