target/s390x: Replace gdb_get_regl() -> gdb_get_reg64()

target/s390x: Replace gdb_get_regl() -> gdb_get_reg64()

We only build s390x targets as 64-bit:

  $ git grep BIT configs/targets/s390x-*
  configs/targets/s390x-linux-user.mak:6:TARGET_LONG_BITS=64
  configs/targets/s390x-softmmu.mak:5:TARGET_LONG_BITS=64

Therefore gdb_get_regl() expands to gdb_get_reg64(). Use
the latter which is more explicit.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
Reviewed-by: Eric Farman <farman@linux.ibm.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-ID: <20251224162036.90404-4-philmd@linaro.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>