dsi_sync_vc() uses in_interrupt() to create a warning if the function is
used in non-preemptible context.

The usage of in_interrupt() in drivers is phased out and Linus clearly
requested that code which changes behaviour depending on context should
either be separated or the context be conveyed in an argument passed by the
caller, which usually knows the context.

The wait_for_completion() function (used in dsi_sync_vc_vp() and
dsi_sync_vc_l4() has already a check if it is invoked from proper
context.

Remove WARN_ON(in_interrupt()) from the driver.

Cc: linux-omap@vger.kernel.org
Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210208223810.388502-3-bigeasy@linutronix.de