uboot-phytec

env: spi: Fix incorrect entry description

Fix the max frequency entry description, it's incorrect.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Chris Brandt <chris.brandt@renesas.com>
Cc: Jagan Teki <jagan@amarulasolutions.com>
Cc: Tom Rini <trini@konsulko.com>