Staging: sm750fb: fix build warning with proc_panDisplay

Change the options to the proc_panDisplay function pointer to match the
function pointer that we want to assign to it, in order to remove the
build warning.

Cc: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Cc: Teddy Wang <teddy.wang@siliconmotion.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>