s390: Fix up *cmp_and_trap_unsigned_int<mode> constraints [PR104775]

The following testcase fails to assemble due to clgte %r6,0(%r1,%r10)
insn not being accepted by assembler.
My rough understanding is that in the RSY-b insn format the spot
in other formats used for index registers is used instead for M3 what
kind of comparison it is, so this patch follows what other similar
instructions use for constraint (i.e. one without index register).

2022-03-07  Jakub Jelinek  <jakub@redhat.com>

	PR target/104775
	* config/s390/s390.md (*cmp_and_trap_unsigned_int<mode>): Use
	S constraint instead of T in the last alternative.

	* gcc.target/s390/pr104775.c: New test.