serial: ifx6x60: Remove superfluous casts when calling request_irq()

There's no need to cast the last parameter of {request,free}_irq() to
"void *", as any pointer type is accepted.

Remove the superfluous casts to fix this.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>