[gdb/testsuite] Add PR number in KFAIL in gdb.ada/array_ptr_renaming.exp

[gdb/testsuite] Add PR number in KFAIL in gdb.ada/array_ptr_renaming.exp

When running test-case gdb.ada/array_ptr_renaming.exp we run into:
...
(gdb) print ntp^M
$3 = (3 => 30, 40)^M
(gdb) KFAIL: gdb.ada/array_ptr_renaming.exp: print ntp (PRMS: gdb/NNNN)
...

I've opened PR25883 for this failure.  Reference the PR from the KFAIL, such
that we have:
...
KFAIL: gdb.ada/array_ptr_renaming.exp: print ntp (PRMS: gdb/25883)
...

gdb/testsuite/ChangeLog:

2020-04-28  Tom de Vries  <tdevries@suse.de>

	* gdb.ada/array_ptr_renaming.exp: Add PR number in KFAIL.