[media] ov13858: remove duplicated const declaration

As reported by gcc:

drivers/media/i2c/ov13858.c:953:20: warning: duplicate const
drivers/media/i2c/ov13858.c:953:14: warning: duplicate 'const' declaration specifier [-Wduplicate-decl-specifier]
 static const const s64 link_freq_menu_items[OV13858_NUM_OF_LINK_FREQS] = {
              ^~~~~

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>