spi/s3c64xx: Add missing static storage class specifiers

Silences the following sparse warnings:
drivers/spi/spi-s3c64xx.c:1482:32: warning:
symbol 's3c2443_spi_port_config' was not declared. Should it be static?
drivers/spi/spi-s3c64xx.c:1489:32: warning:
symbol 's3c6410_spi_port_config' was not declared. Should it be static?
drivers/spi/spi-s3c64xx.c:1495:32: warning:
symbol 's5p64x0_spi_port_config' was not declared. Should it be static?
drivers/spi/spi-s3c64xx.c:1501:32: warning:
symbol 's5pc100_spi_port_config' was not declared. Should it be static?
drivers/spi/spi-s3c64xx.c:1508:32: warning:
symbol 's5pv210_spi_port_config' was not declared. Should it be static?
drivers/spi/spi-s3c64xx.c:1515:32: warning:
symbol 'exynos4_spi_port_config' was not declared. Should it be static?

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>