mtd: spear_smi: Drop if with an always false condition

The remove callback is only called after probe completed successfully.
In this case platform_set_drvdata() was called with a non-NULL argument
and so dev is never NULL.

This is a preparation for making platform remove callbacks return void.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20220603210758.148493-8-u.kleine-koenig@pengutronix.de