spi: Remove CONFIG_OF_SPI_FLASH

Previous patches removed the last usages of this config variable, so
that it is now obsolete.

This patch removes it from the whitelist.
Reviewed-by: NSimon Glass <sjg@chromium.org>
Reviewed-by: NJagan Teki <jagan@openedev.com>
Signed-off-by: NMario Six <mario.six@gdsys.cc>

scripts/config_whitelist.txt

@@ -1554,7 +1554,6 @@ CONFIG_NUM_PAMU
 CONFIG_ODROID_REV_AIN
 CONFIG_OFF_PADCONF
 CONFIG_OF_
-CONFIG_OF_SPI_FLASH
 CONFIG_OF_STDOUT_PATH
 CONFIG_OMAP_EHCI_PHY1_RESET_GPIO
 CONFIG_OMAP_EHCI_PHY2_RESET_GPIO