drm/tilcdc: avoid 'make W=2' build failure

The -Wmissing-field-initializer warning when building with W=2
turns into an error because tilcdc is built with -Werror:

drm/tilcdc/tilcdc_drv.c:431:33: error: missing field 'data' initializer [-Werror,-Wmissing-field-initializers] { "regs", tilcdc_regs_show, 0 },
drm/tilcdc/tilcdc_drv.c:432:33: error: missing field 'data' initializer [-Werror,-Wmissing-field-initializers] { "mm",   tilcdc_mm_show,   0 },

Add the missing field initializers to address the warning.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Jyri Sarha <jsarha@ti.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201026194110.3817470-1-arnd@kernel.org