auxdisplay: charlcd: Partially revert "Move hwidth and bwidth to struct hd44780_common"

Commit 2545c1c9 ("auxdisplay: Move hwidth and bwidth to struct
hd44780_common") makes charlcd_alloc() argument-less effectively dropping
the single allocation for the struct charlcd_priv object along with
the driver specific one. Restore that behaviour here.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>