mfd: dln2: Remove the unneeded include <linux/i2c.h>

This driver does not use i2c, so there is no point in including
<linux/i2c.h>

Remove it.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/baf28e7f0fb57e918b76eaa92b94a2ae1a02cce0.1682318879.git.christophe.jaillet@wanadoo.fr