jtag_scan: updated JTAG_MAX_IR_LEN to be the max bit-length of the IR…

… storage, even though it's not large enough for all Xilinx devices

src/target/jtag_scan.h

@@ -27,7 +27,7 @@
 #include "jtagtap.h"
 
 #define JTAG_MAX_DEVS   32U
-#define JTAG_MAX_IR_LEN 38U
+#define JTAG_MAX_IR_LEN 32U /* NOTE: This is not long enough for all Xilinx devices */
 
 typedef struct jtag_dev {
 	uint32_t jd_idcode;