drm/panel: nt35510: Do not fail if DSI read fails

Failing to read the MTP over DSI should not bring down the
system and make us bail out from using the display, it turns
out that this happens when toggling the display off and on,
and that write is often still working so the display output
is just fine. Printing an error is enough.

Tested by killing the Gnome session repeatedly on the
Samsung Skomer.

Fixes: 899f24ed

 ("drm/panel: Add driver for Novatek NT35510-based panels")
Cc: Stephan Gerhold <stephan@gerhold.net>
Reported-by:  <newbyte@disroot.org>
Acked-by: Stefan Hansson <newbyte@disroot.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210603231830.3200040-1-linus.walleij@linaro.org