shields: st_b_lcd40_dsi1_mb1166: bump up display init priority

MIPI-DSI initialization priority got delayed in fed377f6, but now
that's at the same priority as the OTM8009A for this board
configuration, and OTM8009A needs MIPI-DSI to be initialized. Being at
the same priority means that it may or may not work depending on the
linking order, this is exposed with:

$ west build -p -b stm32h747i_disco_m7 samples/subsys/display/lvgl \
		-DSHIELD=st_b_lcd40_dsi1_mb1166 \
		-DCONFIG_CHECK_INIT_PRIORITIES=y
...
WARNING: /soc/dsihost@50000000/otm8009a@0 POST_KERNEL 86 ==
	/soc/dsihost@50000000 POST_KERNEL 86

Bumping the display priority up to make sure it still works.

Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>