mmc: mmci: Don't pretend all variants to have MCI_STARBITERR flag

This patch prepares for supporting the STM32 variant that
has no such bit in the status register.

Signed-off-by: Andrea Merello <andrea.merello@gmail.com>
Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>