ARM: da850evm: Fix broken SPI Flash

A previous patch converted a bunch of settings for CONFIG_SF_DEFAULT
but it broke the SPI Flash which now prevents booting.  This patch
now correctly sets CONFIG_SF_DEFAULT_SPEED=30000000 to match what it
was before the conversion.

Fixes: 14453fbfadc2 ("Convert CONFIG_SF_DEFAULT_* to Kconfig")

Signed-off-by: Adam Ford <aford173@gmail.com>
diff --git a/configs/da850evm_defconfig b/configs/da850evm_defconfig
index 4b09ba1..745ae2b 100644
--- a/configs/da850evm_defconfig
+++ b/configs/da850evm_defconfig
@@ -55,6 +55,7 @@
 CONFIG_MTD_DEVICE=y
 CONFIG_DM_SPI_FLASH=y
 CONFIG_SPI_FLASH=y
+CONFIG_SF_DEFAULT_SPEED=30000000
 CONFIG_SPI_FLASH_STMICRO=y
 CONFIG_SPI_FLASH_WINBOND=y
 CONFIG_SPI_FLASH_MTD=y