auxdisplay: charlcd: checking for pointer reference before dereferencing

Check if the pointer lcd->ops->init_display exists before dereferencing it.
If a driver called charlcd_init() without defining the ops, this would
return segmentation fault, as happened to me when implementing a charlcd
driver.  Checking the pointer before dereferencing protects from
segmentation fault.

Signed-off-by: Luiz Sampaio <sampaio.ime@gmail.com>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>