tty: mmc: sdio: use bool for cts and remove parentheses

'cts' in sdio_uart_check_modem_status() is considered a 'bool', but
typed as signed 'int'. Make it 'bool' so it is clear the code does not
care about the masked value, but true/false.

Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/20250317070046.24386-18-jirislaby@kernel.org


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>