board: stm32mp1: change dfu function to static

Change the dfu functions dfu_otp_read and dfu_pmic_read to static,
this patch avoids warning when compiling with W=1.
Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@st.com>

board/st/stm32mp1/stm32mp1.c

@@ -1012,7 +1012,7 @@ void set_dfu_alt_info(char *interface, char *devstr)
 #include <dfu.h>
 #include <power/stpmic1.h>
 
-int dfu_otp_read(u64 offset, u8 *buffer, long *size)
+static int dfu_otp_read(u64 offset, u8 *buffer, long *size)
 {
 	struct udevice *dev;
 	int ret;
@@ -1032,7 +1032,7 @@ int dfu_otp_read(u64 offset, u8 *buffer, long *size)
 	return 0;
 }
 
-int dfu_pmic_read(u64 offset, u8 *buffer, long *size)
+static int dfu_pmic_read(u64 offset, u8 *buffer, long *size)
 {
 	int ret;
 #ifdef CONFIG_PMIC_STPMIC1