mtd: spi-nor: Compile files in controllers/ directory

Commit a0900d0 ("mtd: spi-nor: Prepare core / manufacturer code
split") moved various files into a new directory, but did not add the new
directory to its parent directory Makefile. The moved files no longer
build, and affected flash chips no longer instantiate.

Adding the new directory to the parent directory Makefile fixes the
problem.

Fixes: a0900d0 ("mtd: spi-nor: Prepare core / manufacturer code split")
Cc: Boris Brezillon <[email protected]>
Cc: Tudor Ambarus <[email protected]>
Signed-off-by: Guenter Roeck <[email protected]>
Reviewed-by: Boris Brezillon <[email protected]>
Acked-by: Joel Stanley <[email protected]>
Reviewed-by: Tudor Ambarus <[email protected]>
Signed-off-by: Richard Weinberger <[email protected]>

drivers/mtd/spi-nor/Makefile

@@ -18,3 +18,5 @@ spi-nor-objs			+= winbond.o
 spi-nor-objs			+= xilinx.o
 spi-nor-objs			+= xmc.o
 obj-$(CONFIG_MTD_SPI_NOR)	+= spi-nor.o
+
+obj-$(CONFIG_MTD_SPI_NOR)	+= controllers/