cirrus_vga: also assign gr0/1 when writting shadow_gr0/1

This is a regression/bug caused by previous vga_cleanup.  This fixes
Ubuntu installer reported by:
	 Pierre Riteau
Signed-off-by: NJuan Quintela <quintela@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

hw/cirrus_vga.c

@@ -1490,9 +1490,11 @@ cirrus_vga_write_gr(CirrusVGAState * s, unsigned reg_index, int reg_value)
 #endif
     switch (reg_index) {
     case 0x00:			// Standard VGA, BGCOLOR 0x000000ff
+	s->vga.gr[reg_index] = reg_value & gr_mask[reg_index];
 	s->cirrus_shadow_gr0 = reg_value;
 	break;
     case 0x01:			// Standard VGA, FGCOLOR 0x000000ff
+	s->vga.gr[reg_index] = reg_value & gr_mask[reg_index];
 	s->cirrus_shadow_gr1 = reg_value;
 	break;
     case 0x02:			// Standard VGA