[media] v4l2-ctrls: Correct v4l2_ctrl_get_int_menu() function's return type

Remove the redundant 'const' qualifiers from the function
signature and from the qmenu_int arrays' declarations.

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>