USB: serial: metro-usb: cosmetic fix in driver description.

Message in kernel log:
"metro-usb ttyUSB0: Metrologic USB to Serial converter now disconnected from ttyUSB0"

bit more likely than:
"metro-usb ttyUSB0: Metrologic USB to serial converter. converter now disconnected from ttyUSB0"

Signed-off-by: Aleksey Babahin <tamerlan311@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>