ARM: S3C64XX: remove obsolete Makefile line

Commit a07613a5 ("Merge branch 'samsung/dt' into samsung/cleanup")
added this line to arch/arm/mach-s3c64xx/Makefile:
    obj-$(CONFIG_S3C64XX_DEV_SPI)	+= dev-spi.o

But at that time CONFIG_S3C64XX_DEV_SPI wasn't a valid Kconfig macro
anymore and arch/arm/mach-s3c64xx/dev-spi.c was already removed. So we
can remove this line.
Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>

arch/arm/mach-s3c64xx/Makefile

@@ -32,7 +32,6 @@ obj-$(CONFIG_S3C64XX_DMA)	+= dma.o
 
 obj-y				+= dev-uart.o
 obj-y				+= dev-audio.o
-obj-$(CONFIG_S3C64XX_DEV_SPI)	+= dev-spi.o
 
 # Device setup