auxdisplay: panel: Fix missing print function pointer

charlcd drivers need to provide some print function to charlcd. For
hd44780 based panel driver this function was missing. We provide the
generic hd44780_common_print function which should be suitable.

Fixes: b26deabb ("auxdisplay: hd44780_common_print")
Reported-by: kernel test robot <oliver.sang@intel.com>
Signed-off-by: Lars Poeschel <poeschel@lemonage.de>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>