m68k: sun3: Replace vsprintf() with bounded vsnprintf()

vsprintf() performs no bounds checking and can overflow - replace it
with the safer vsnprintf().

Also remove the useless '+ 1' that is a leftover of commit 66ed28ea096c
("m68k: sun3: Remove unused vsprintf() return value in prom_printf()").

Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://patch.msgid.link/20260117202152.1036278-2-thorsten.blum@linux.dev
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

arch/m68k/sun3/prom/printf.c

diff --git a/arch/m68k/sun3/prom/printf.c b/arch/m68k/sun3/prom/printf.c
index db5537e..cb4934d 100644
--- a/arch/m68k/sun3/prom/printf.c
+++ b/arch/m68k/sun3/prom/printf.c
@@ -30,9 +30,9 @@ prom_printf(char *fmt, ...)
 
 #ifdef CONFIG_KGDB
 	ppbuf[0] = 'O';
-	vsprintf(ppbuf + 1, fmt, args) + 1;
+	vsnprintf(ppbuf + 1, sizeof(ppbuf) - 1, fmt, args);
 #else
-	vsprintf(ppbuf, fmt, args);
+	vsnprintf(ppbuf, sizeof(ppbuf), fmt, args);
 #endif
 
 	bptr = ppbuf;