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_def.h b/plat/st/stm32mp1/stm32mp1_def.h
index fd12159..aabe81f 100644
--- a/plat/st/stm32mp1/stm32mp1_def.h
+++ b/plat/st/stm32mp1/stm32mp1_def.h
@@ -429,7 +429,7 @@
 #define TAMP_BKP_REGISTER_BASE		(TAMP_BASE + U(0x100))
 
 #if !(defined(__LINKER__) || defined(__ASSEMBLER__))
-static inline uint32_t tamp_bkpr(uint32_t idx)
+static inline uintptr_t tamp_bkpr(uint32_t idx)
 {
 	return TAMP_BKP_REGISTER_BASE + (idx << 2);
 }