mtd: rawnand: nandsim: Merge repeat codes in ns_switch_state

The moving block of codes is shared between both 'if' and 'else' condition,
we can move it out to reduce the duplication.

Signed-off-by: RinHizakura <s921975628@gmail.com>
Reviewed-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20211225100648.119011-1-s921975628@gmail.com