auxdisplay: img-ascii-lcd: fix typo on select SYSCON/MFD_SYSCON

img-ascii-lcd select un-existing SYSCON kconfig name.
This patch fix this error by using the correct MFD_SYSCON kconfig name.

Signed-off-by: Corentin Labbe <clabbe.montjoie@gmail.com>
Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>