Boot : Fix boot_platform_quit

According to compiler and optimization:
- registers used to retrieve vt_cpy are pushed in sp,
- sp is modified before calling boot_jump_to_next_image(i.e if some
non scratch registers have been used),this creates an incorrect sp.

Change-Id: I866ac756d3611f67636b99b10d340c77dd12b148
Signed-off-by: Michel Jaouen <michel.jaouen@st.com>
diff --git a/platform/ext/common/boot_hal.c b/platform/ext/common/boot_hal.c
index 50a6834..a005b73 100644
--- a/platform/ext/common/boot_hal.c
+++ b/platform/ext/common/boot_hal.c
@@ -85,7 +85,7 @@
      */
     __set_MSPLIM(0);
 #endif
-    __set_MSP(vt->msp);
+    __set_MSP(vt_cpy->msp);
     __DSB();
     __ISB();
 
diff --git a/platform/ext/target/stm/stm32l5xx/bl2/boot_hal.c b/platform/ext/target/stm/stm32l5xx/bl2/boot_hal.c
index f14008a..8df0015 100644
--- a/platform/ext/target/stm/stm32l5xx/bl2/boot_hal.c
+++ b/platform/ext/target/stm/stm32l5xx/bl2/boot_hal.c
@@ -86,7 +86,7 @@
      */
     __set_MSPLIM(0);
 #endif
-    __set_MSP(vt->msp);
+    __set_MSP(vt_cpy->msp);
     __DSB();
     __ISB();