__put_user can write bytes, words (2 bytes) or longwords (4 bytes).
Here obviously words should have been written, but bytes were written,
so values like 0x9c5f were truncated to 0x5f.

Fix this by changing retcode from uint8_t to to uint16_t in
target_signal_frame and also in the unused rt_signal_frame.

This problem was reported by static code analysis (smatch).

Cc: qemu-stable@nongnu.org
Signed-off-by: NStefan Weil <sw@weilnetz.de>
Acked-by: NRiku Voipio <riku.voipio@linaro.org>
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Tested-by: NEdgar E. Iglesias <edgar.iglesias@xilinx.com>
Reviewed-by: NEdgar E. Iglesias <edgar.iglesias@xilinx.com>
Signed-off-by: NEdgar E. Iglesias <edgar.iglesias@xilinx.com>