software/libbase: Remove empty printf statements

To fix compiler warnings of the following type:

    warning: zero-length gnu_printf format string [-Wformat-zero-length]

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

litex/soc/software/libbase/exception.c

@@ -156,7 +156,6 @@ static void gdb_stub(unsigned long pc, unsigned long sr,
 			}
 
 			default:
-				snprintf(buf, sizeof(buf), "");
 				break;
 		}
 

litex/soc/software/libbase/progress.c

@@ -61,6 +61,4 @@ void init_progression_bar(int max)
 	spin = 0;
 	if (progress_max && progress_max != FILESIZE_MAX)
 		printf("[%*s]\r[", HASHES_PER_LINE, "");
-	else
-		printf("");
 }