refactor(stm32mp1): update tamp_bkpr return type

tamp_bkpr() returns a register address. So use uintptr_t instead of
uin32_t.

Signed-off-by: Nicolas Toromanoff <nicolas.toromanoff@foss.st.com>
Change-Id: I5eddfa525465313dadfec18d128248a968ba74e2
diff --git a/plat/st/stm32mp1/stm32mp1_private.c b/plat/st/stm32mp1/stm32mp1_private.c
index 9b39b9d..1125a69 100644
--- a/plat/st/stm32mp1/stm32mp1_private.c
+++ b/plat/st/stm32mp1/stm32mp1_private.c
@@ -568,7 +568,7 @@
 
 void stm32_save_boot_interface(uint32_t interface, uint32_t instance)
 {
-	uint32_t bkpr_itf_idx = tamp_bkpr(TAMP_BOOT_MODE_BACKUP_REG_ID);
+	uintptr_t bkpr_itf_idx = tamp_bkpr(TAMP_BOOT_MODE_BACKUP_REG_ID);
 
 	clk_enable(RTCAPB);
 
@@ -585,7 +585,7 @@
 	static uint32_t itf;
 
 	if (itf == 0U) {
-		uint32_t bkpr = tamp_bkpr(TAMP_BOOT_MODE_BACKUP_REG_ID);
+		uintptr_t bkpr = tamp_bkpr(TAMP_BOOT_MODE_BACKUP_REG_ID);
 
 		clk_enable(RTCAPB);