drm/sti: Add __iomem for mixer_dbg_mxn's parameter

Sparse complains about incorrect type in argument 1.
expected void const volatile __iomem *ptr but got void *.
so modify mixer_dbg_mxn's addr parameter.

Reported-by: kernel test robot <[e-mail]>
Closes: https://lore.kernel.org/oe-kbuild-all/[e-mail]/
Fixes: a5f81078a56c ("drm/sti: add debugfs entries for MIXER crtc")
Signed-off-by: Pei Xiao <[e-mail]>
Acked-by: Raphael Gallais-Pou <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/c[e-mail]
Signed-off-by: Raphael Gallais-Pou <[e-mail]>

drivers/gpu/drm/sti/sti_mixer.c

···
 	}
 }
 
-static void mixer_dbg_mxn(struct seq_file *s, void *addr)
+static void mixer_dbg_mxn(struct seq_file *s, void __iomem *addr)
 {
 	int i;