stm32mp2: Fix CONFIG_STM32MP25X flag usage

"#if" was used instead of "#ifdef"

Fixes: 01a701994b05 ("stm32mp2: initial support")
Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>
Reviewed-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
diff --git a/arch/arm/mach-stm32mp/include/mach/stm32.h b/arch/arm/mach-stm32mp/include/mach/stm32.h
index f598da9..6eb85ba 100644
--- a/arch/arm/mach-stm32mp/include/mach/stm32.h
+++ b/arch/arm/mach-stm32mp/include/mach/stm32.h
@@ -157,7 +157,7 @@
 #endif /* __ASSEMBLY__ */
 #endif /* CONFIG_STM32MP15X || CONFIG_STM32MP13X */
 
-#if CONFIG_STM32MP25X
+#ifdef CONFIG_STM32MP25X
 #define STM32_RCC_BASE			0x44200000
 #define STM32_TAMP_BASE			0x46010000