ifdtool: Add SPI_FREQUENCY_50MHZ_30MHZ as a valid freq

Without this change, error "Unknown descriptor version: 4" will be
returned if this frequency is selected (seen on GLKRVP)

Change-Id: Ib5bfb996b85c7245d8f9c70988bfd5bbac882d74
Signed-off-by: Hannah Williams <hannah.williams@intel.com>
Reviewed-on: https://review.coreboot.org/18688
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Tested-by: build bot (Jenkins)
1 file changed