[media] v4l: omap4iss: configuration using uninitialized variable

Variable reg is not initialized.
Random values are written to OMAP4 ISS registers if !ctx->eof_enabled.

Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>