MLK-9842 mtd: fsl-quadspi: Propagate the error from of_modalias_node()

The 'map_failed' label will return 'ret', so we need to assign the error
code to 'ret', otherwise the probe function will return success.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Huang Shijie <shijie8@gmail.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
(cherry picked from commit b26171e3)
(cherry picked from commit 9e4a091d30e27dd40a04b892bf5f6bf372271380)