mtd: spi-nor: fix "No newline at end of file"

Add a newline to the end of drivers/spi-nor/Makefile to get rid the message,
"No newline at end of file", produced by git. This fix will allow subsequent
changes to the file to be able to produce clean patches.

Signed-off-by: Matthew Gerlach <matthew.gerlach@linux.intel.com>
Signed-off-by: Cyrille Pitchen <cyrille.pitchen@wedev4u.fr>