serial, kconfig: fix menutext

fix menutext for the options SPL_DM_SERIAL and TPL_DM_SERIAL.
Both have the same text as DM_SERIAL, which is
confusing.

Signed-off-by: Heiko Schocher <hs@denx.de>
Reviewed-by: Stefan Roese <sr@denx.de>
1 file changed