stm32mp1: Fix warning display when 1.5A power supply is used

On DK1/2 board, when a 1.5A power supply is detected, a warning
message is displayed. In this message, "1.5mA" is displayed instead
of "1.5A".

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Reviewed-by: Patrick Delaunay <patrick.delaunay@st.com>