ARM: s3c: Rename s3c64xx_spi_setname() function

The name s3c64xx_spi_setname() suggests it is shared with S3C64xx
platform, but except of contents it is not.  It is called only by
S3C24xx code, so make it clear in the name.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>