Don't mark static functions as kernel-doc.

Prevents multiple kernel-doc build warnings:

drivers/gpu/drm/sti/sti_hdmi.c:187: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 * HDMI interrupt handler threaded
drivers/gpu/drm/sti/sti_hdmi.c:219: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 * HDMI interrupt handler
drivers/gpu/drm/sti/sti_hdmi.c:241: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 * Set hdmi active area depending on the drm display mode selected
drivers/gpu/drm/sti/sti_hdmi.c:262: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 * Overall hdmi configuration
drivers/gpu/drm/sti/sti_hdmi.c:340: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 * Helper to concatenate infoframe in 32 bits word
drivers/gpu/drm/sti/sti_hdmi.c:357: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 * Helper to write info frame
drivers/gpu/drm/sti/sti_hdmi.c:427: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 * Prepare and configure the AVI infoframe
drivers/gpu/drm/sti/sti_hdmi.c:470: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 * Prepare and configure the AUDIO infoframe
drivers/gpu/drm/sti/sti_hdmi.c:555: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 * Software reset of the hdmi subsystem

Fixes: 5402626c ("drm: sti: add HDMI driver")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Aditya Srivastava <yashsri421@gmail.com>
Cc: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Cc: Alain Volmat <alain.volmat@foss.st.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Acked-by: Alain Volmat <alain.volmat@foss.st.com>
Signed-off-by: Philippe Cornu <philippe.cornu@foss.st.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220326235132.25192-1-rdunlap@infradead.org