mtd: onenand: Use a better name for samsung driver

Commit 55ed51ff ("{tty: serial, nand: onenand}: samsung: rename to
fix build warning") has changed the samsung.c driver to be
samsung_mtd.c in order to avoid a conflict in module names with the
tty driver.

Since the *_mtd suffix is very undescriptive, rename it to
onenand_samsung.c, following the folder's convention. Same will be
applied to the omap2 onenand driver.
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>

drivers/mtd/nand/onenand/Makefile

@@ -9,6 +9,6 @@ obj-$(CONFIG_MTD_ONENAND)		+= onenand.o
 # Board specific.
 obj-$(CONFIG_MTD_ONENAND_GENERIC)	+= generic.o
 obj-$(CONFIG_MTD_ONENAND_OMAP2)		+= omap2.o
-obj-$(CONFIG_MTD_ONENAND_SAMSUNG)       += samsung_mtd.o
+obj-$(CONFIG_MTD_ONENAND_SAMSUNG)       += onenand_samsung.o
 
 onenand-objs = onenand_base.o onenand_bbt.o