video: fbdev: of: display_timing: Remove a redundant zeroing of memory

of_parse_display_timing() already call memset(0) on its 2nd argument, so
there is no need to clear it explicitly before calling this function.

Use kmalloc() instead of kzalloc() to save a few cycles.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Helge Deller <deller@gmx.de>