mtd: rawnand: fsl_ifc: check result of SRAM initialization

The SRAM initialization might fail. If that happens further NAND operations
won't be successful. Therefore, the chip init routine should fail if the SRAM
initialization didn't work.

Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>