OpenOCD: drop comparison with true/false

Fix checkpatch errors:

	ERROR:BOOL_COMPARISON: Using comparison to true/false is
	error prone

While there,
- drop useless parenthesis,
- drop unnecessary else after a return.

Change-Id: I1234737b3e65bd10df5e938d1c36f9abaf02d348
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/8496
Reviewed-by: zapb <dev@zapb.de>
Tested-by: jenkins

src/target/cortex_m.c

@@ -1521,7 +1521,7 @@ static int cortex_m_step(struct target *target, int current,
 	/* if no bkpt instruction is found at pc then we can perform
 	 * a normal step, otherwise we have to manually step over the bkpt
 	 * instruction - as such simulate a step */
-	if (bkpt_inst_found == false) {
+	if (!bkpt_inst_found) {
 		if (cortex_m->isrmasking_mode != CORTEX_M_ISRMASK_AUTO) {
 			/* Automatic ISR masking mode off: Just step over the next
 			 * instruction, with interrupts on or off as appropriate. */