hwmon: (dell-smm) Fix off-by-one error in dell_smm_is_visible()

hwmon: (dell-smm) Fix off-by-one error in dell_smm_is_visible()

The documentation states that on machines supporting only global
fan mode control, the pwmX_enable attributes should only be created
for the first fan channel (pwm1_enable, aka channel 0).

Fix the off-by-one error caused by the fact that fan channels have
a zero-based index.

Cc: stable@vger.kernel.org
Fixes: 1c1658058c99 ("hwmon: (dell-smm) Add support for automatic fan mode")
Signed-off-by: Armin Wolf <W_Armin@gmx.de>
Link: https://lore.kernel.org/r/20251203202109.331528-1-W_Armin@gmx.de
Signed-off-by: Guenter Roeck <linux@roeck-us.net>