serial: 8250: remove return statements from void function

serial8250_set_mctrl() is a void type function.  Returning something
does not look nice.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
1 file changed