media: omap3isp/isp: remove an unused static var

The isp_xclk_init_data const data isn't used anywere.

drivers/media/platform/omap3isp/isp.c:294:35: warning: ‘isp_xclk_init_data’ defined but not used [-Wunused-const-variable=]
 static const struct clk_init_data isp_xclk_init_data = {
                                   ^~~~~~~~~~~~~~~~~~

Fixes: 9b28ee3c ("[media] omap3isp: Use the common clock framework")

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>