tree: Replace union {0} initializers with {} for C23 compliance

This change addresses GCC-15 behavior where {0} union initializers only
clear the first member, leaving padding bits uninitialized. The new {}
initializer ensures full union clearing as required by C23.

Change-Id: I1d9b063d8bdd3d2f0b0f67e6c20eb484ff6a5cc5
Signed-off-by: Elyes Haouas <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/88732
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Yidi Lin <yidilin@google.com>
Reviewed-by: Yu-Ping Wu <yupingso@google.com>

payloads/libpayload/curses/PDCurses/dos/pdcutil.c

@@ -88,7 +88,7 @@ void setdosmemword(int offset, unsigned short w)
 
 void PDC_dpmi_int(int vector, pdc_dpmi_regs *rmregs)
 {
-    union REGPACK regs = {0};
+    union REGPACK regs = {};
 
     rmregs->w.ss = 0;
     rmregs->w.sp = 0;

src/drivers/wifi/generic/acpi.c

@@ -1246,7 +1246,7 @@ static void wifi_ssdt_write_properties(const struct device *dev, const char *sco
 	struct dsm_uuid dsm_ids[MAX_DSM_FUNCS];
 
 	/* Retrieve the SAR limits data */
-	union wifi_sar_limits sar_limits = {0};
+	union wifi_sar_limits sar_limits = {};
 	bool sar_loaded = false;
 	if (CONFIG(USE_SAR)) {
 		if (get_wifi_sar_limits(&sar_limits) < 0)

src/soc/mediatek/common/dp/dptx_common.c

@@ -356,7 +356,7 @@ static void dptx_set_tu(struct mtk_dp *mtk_dp)
 static void dptx_set_misc(struct mtk_dp *mtk_dp)
 {
 	u8 format, depth;
-	union misc_t dptx_misc = { .cmisc = {0} };
+	union misc_t dptx_misc = { .cmisc = {} };
 
 	format = mtk_dp->info.format;
 	depth = mtk_dp->info.depth;