hwmon: (powerz) Fix missing usb_kill_urb() on signal interrupt

hwmon: (powerz) Fix missing usb_kill_urb() on signal interrupt

wait_for_completion_interruptible_timeout() returns -ERESTARTSYS when
interrupted. This needs to abort the URB and return an error. No data
has been received from the device so any reads from the transfer
buffer are invalid.

The original code tests !ret, which only catches the timeout case (0).
On signal delivery (-ERESTARTSYS), !ret is false so the function skips
usb_kill_urb() and falls through to read from the unfilled transfer
buffer.

Fix by capturing the return value into a long (matching the function
return type) and handling signal (negative) and timeout (zero) cases
with separate checks that both call usb_kill_urb() before returning.

Fixes: 4381a36abdf1c ("hwmon: add POWER-Z driver")
Cc: stable@vger.kernel.org
Signed-off-by: Sanman Pradhan <psanman@juniper.net>
Link: https://lore.kernel.org/r/20260410002521.422645-3-sanman.pradhan@hpe.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>