drivers/jlink: fix check for max prescaler

drivers/jlink: fix check for max prescaler

The value stored in TPIU ACPR is the prescaler value decremented
by one. Thus, the test should verify that prescaler does not
exceed the maximum ACPR value plus one. Also, zero value is not
allowed for prescaler.

Change-Id: I1817f04f2a310b2f413bad726f0cb9dd6a4172e2
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/5907
Tested-by: jenkins
Reviewed-by: Adrian M Negreanu <adrian.negreanu@nxp.com>