usbip: vudc: Convert snprintf() to sysfs_emit()

Coccinnelle reports a warning
Warning: Use scnprintf or sprintf

Following the advice on kernel documentation
https://www.kernel.org/doc/html/latest/filesystems/sysfs.html

For show(device *...) functions we should only use sysfs_emit() or sysfs_emit_at()
especially when formatting the value to be returned to user space.
Convert snprintf() to sysfs_emit()

Signed-off-by: Jules Irenge <jules.irenge@postgrad.manchester.ac.uk>
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
Link: https://lore.kernel.org/r/YzhVIaNGdM33pcts@octinomon
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>