Build system: Remove a trailing tab from gpio/Makefile

emacs complains about this line, because it thinks lines with just a
tab on in Makefiles are suspicious.  Remove the needless tab.

No functional change.

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>

gpio/Makefile

@@ -54,7 +54,7 @@ version.h:	../VERSION
 gpio:	$(OBJ)
 	$Q echo [Link]
 	$Q $(CC) -o $@ $(OBJ) $(LDFLAGS) $(LIBS)
-	
+
 .c.o:
 	$Q echo [Compile] $<
 	$Q $(CC) -c $(CFLAGS) $< -o $@