arm_adi_v5: use macro DP_APSEL_MAX in place of magic number

arm_adi_v5: use macro DP_APSEL_MAX in place of magic number

Commit 11019a824d02 ("adi_v5: enforce check on AP number value")
introduces the macro DP_APSEL_MAX and use it in place of hardcoded
magic numbers for the upper limit of AP selection value.

Fix one more place where the macro should be used.

Change-Id: I6c57f72405c69bbb40924221309d95dfeb5f7540
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Fixes: 11019a824d02 ("adi_v5: enforce check on AP number value")
Reviewed-on: http://openocd.zylin.com/6415
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>
Tested-by: jenkins
Reviewed-by: Tarek BOCHKATI <tarek.bouchkati@gmail.com>