drm/bridge: nwl-dsi: Remove superfluous write to NWL_DSI_IRQ_MASK register

To initialize register NWL_DSI_IRQ_MASK, it's enough to write it
only once in function nwl_dsi_init_interrupts().

Signed-off-by: Liu Ying <victor.liu@nxp.com>
Reviewed-by: Guido Günther <agx@sigxcpu.org>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220216085842.1973868-1-victor.liu@nxp.com