mtd: spear_smi: use GFP_KERNEL

Platform_driver probe functions aren't called with locks held
and thus don't need GFP_ATOMIC. Use GFP_KERNEL instead.

Problem found with Coccinelle.

Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20220210204223.104181-8-Julia.Lawall@inria.fr