USB: usbtmc: use interruptible sleep in usbtmc_read

usbtmc_read() calls usbtmc_generic_read()
which uses interruptible sleep, but usbtmc_read()
itself uses uninterruptble sleep for mutual exclusion
between threads. That makes no sense.
Both should use interruptible sleep.

Fixes: 5b775f6 ("USB: add USB test and measurement class driver")
Cc: stable <stable@kernel.org>
Signed-off-by: Oliver Neukum <oneukum@suse.com>
Link: https://lore.kernel.org/r/20250430134810.226015-1-oneukum@suse.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: oneukum

drivers/usb/class/usbtmc.c

@@ -1380,7 +1380,10 @@ static ssize_t usbtmc_read(struct file *filp, char __user *buf,
 	if (!buffer)
 		return -ENOMEM;
 
-	mutex_lock(&data->io_mutex);
+	retval = mutex_lock_interruptible(&data->io_mutex);
+	if (retval < 0)
+		goto exit_nolock;
+
 	if (data->zombie) {
 		retval = -ENODEV;
 		goto exit;
@@ -1503,6 +1506,7 @@ static ssize_t usbtmc_read(struct file *filp, char __user *buf,
 
 exit:
 	mutex_unlock(&data->io_mutex);
+exit_nolock:
 	kfree(buffer);
 	return retval;
 }