sf: Rename sf_ops.c to spi-flash.c

Since all spi-flash core operations are moved into
sf_ops.c then it's better to renamed as spi-flash.c

Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Jagan Teki <jteki@openedev.com>
diff --git a/drivers/mtd/spi/Makefile b/drivers/mtd/spi/Makefile
index a24f761..c665836 100644
--- a/drivers/mtd/spi/Makefile
+++ b/drivers/mtd/spi/Makefile
@@ -12,7 +12,7 @@
 obj-$(CONFIG_SPL_SPI_BOOT)	+= fsl_espi_spl.o
 endif
 
-obj-$(CONFIG_SPI_FLASH) += sf_probe.o sf_ops.o sf_params.o sf.o
+obj-$(CONFIG_SPI_FLASH) += sf_probe.o spi_flash.o sf_params.o sf.o
 obj-$(CONFIG_SPI_FLASH_DATAFLASH) += sf_dataflash.o
 obj-$(CONFIG_SPI_FLASH_MTD) += sf_mtd.o
 obj-$(CONFIG_SPI_FLASH_SANDBOX) += sandbox.o