libmach: change three more BGET macro invocations back

Various compilers complain about the macro expansion not
being used. I fixed a few yesterday. More today.

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/13643044

src/libmach/5obj.c

@@ -127,7 +127,7 @@ addr(Biobuf *bp)
 		break;
 	case D_REGREG:
 	case D_REGREG2:
-		BGETC(bp);
+		Bgetc(bp);
 		break;
 	case D_CONST2:
 		Bgetle4(bp); // fall through
@@ -167,5 +167,5 @@ static void
 skip(Biobuf *bp, int n)
 {
 	while (n-- > 0)
-		BGETC(bp);
+		Bgetc(bp);
 }

src/libmach/6obj.c

@@ -169,5 +169,5 @@ static void
 skip(Biobuf *bp, int n)
 {
 	while (n-- > 0)
-		BGETC(bp);
+		Bgetc(bp);
 }

src/libmach/8obj.c

@@ -166,5 +166,5 @@ static void
 skip(Biobuf *bp, int n)
 {
 	while (n-- > 0)
-		BGETC(bp);
+		Bgetc(bp);
 }