remove gccism from com(4)

[Miod Vallat]

`return f()' when f is a void function is not allowed by the C standard
but is a gcc extension.

Index: com.c
===================================================================
RCS file: /OpenBSD/src/sys/dev/ic/com.c,v
retrieving revision 1.173
diff -u -p -r1.173 com.c
--- com.c       14 Aug 2020 18:14:11 -0000      1.173
+++ com.c       6 May 2021 19:55:13 -0000
@@ -1609,9 +1609,9 @@ com_write_reg(struct com_softc *sc, bus_
        reg <<= sc->sc_reg_shift;
 
        if (sc->sc_reg_width == 4)
-               return bus_space_write_4(sc->sc_iot, sc->sc_ioh, reg, value);
+               bus_space_write_4(sc->sc_iot, sc->sc_ioh, reg, value);
        else
-               return bus_space_write_1(sc->sc_iot, sc->sc_ioh, reg, value);
+               bus_space_write_1(sc->sc_iot, sc->sc_ioh, reg, value);
 }
 
 #ifdef COM_CONSOLE
@@ -1636,9 +1636,9 @@ comcn_write_reg(bus_size_t reg, uint8_t 
        reg <<= comcons_reg_shift;
 
        if (comcons_reg_width == 4)
-               return bus_space_write_4(comconsiot, comconsioh, reg, value);
+               bus_space_write_4(comconsiot, comconsioh, reg, value);
        else
-               return bus_space_write_1(comconsiot, comconsioh, reg, value);
+               bus_space_write_1(comconsiot, comconsioh, reg, value);
 }
 
 #endif