Makefile: simplify two rules

Simplify access to $CONFIG_RAMSIZE. Actually, the previous way
was not working for me, as my $SHELL is not bash.

The bug is uncovered by the next commit, because the "-s" argument
to genramvhd has always been wrong for me, but I didn't notice
(so maybe the "-s" argument has no effect? I can't tell at this point)

Signed-off-by: Alessandro Rubini <rubini@gnudd.com>

Makefile

@@ -139,10 +139,10 @@ config.o: .config
 	./tools/genraminit $*.bin 0 > $@
 
 %.vhd: tools %.bin
-	./tools/genramvhd -s `. ./.config; echo $$CONFIG_RAMSIZE` $*.bin > $@
+	./tools/genramvhd -s $(CONFIG_RAMSIZE) $*.bin > $@
 
 %.mif: tools %.bin
-	./tools/genrammif $*.bin `. ./.config; echo $$CONFIG_RAMSIZE` > $@
+	./tools/genrammif $*.bin $(CONFIG_RAMSIZE) > $@
 
 $(AUTOCONF): silentoldconfig