stm32mp1: correct plat_crash_console_flush()

The base address of UART peripheral should be given in R0, not in R1.
Else the console_stm32_core_flush issues an assert messages due to
recent changes in console flush functions.

Change-Id: Iead01986fdbbf30ad2fd9fa515a1d2b611b4e591
Signed-off-by: Yann Gautier <yann.gautier@st.com>
Reviewed-on: https://gerrit.st.com/c/mpu/oe/st/tf-a/+/187619


Reviewed-by: CITOOLS <smet-aci-reviews@lists.codex.cro.st.com>
Reviewed-by: CIBUILD <smet-aci-builds@lists.codex.cro.st.com>
Reviewed-by: Lionel DEBIEVE <lionel.debieve@st.com>