s390x/tcg: Fix LDER instruction format

s390x/tcg: Fix LDER instruction format

It's RRE, not RXE.

Found by running valgrind's none/tests/s390x/bfp-2.

Fixes: 86b59624c4aa ("s390x/tcg: Implement LOAD LENGTHENED short HFP to long HFP")
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Message-Id: <20230511134726.469651-1-iii@linux.ibm.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>
(cherry picked from commit 970641de01908dd09b569965e78f13842e5854bc)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
(Mjt: context tweak)