hw/input/tsc210x: Fix building with no verbosity

hw/input/tsc210x: Fix building with no verbosity

When building with TSC_VERBOSE not defined, we get:
      CC      arm-softmmu/hw/input/tsc210x.o
    hw/input/tsc210x.c: In function ‘tsc2102_data_register_write’:
    hw/input/tsc210x.c:554:5: error: label at end of compound statement
         default:
         ^~~~~~~
    hw/input/tsc210x.c: In function ‘tsc2102_control_register_write’:
    hw/input/tsc210x.c:638:5: error: label at end of compound statement
         bad_reg:
         ^~~~~~~
    hw/input/tsc210x.c: In function ‘tsc2102_audio_register_write’:
    hw/input/tsc210x.c:766:5: error: label at end of compound statement
         default:
         ^~~~~~~
    make[1]: *** [rules.mak:69: hw/input/tsc210x.o] Error 1

Fix this by replacing the culprit fprintf(stderr) calls by a more
recent API: qemu_log_mask(LOG_GUEST_ERROR). Other fprintf() calls
are left untouched.

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Message-Id: <20190204204517.23698-1-philmd@redhat.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>