util/nvmutil: only swap/copy if checksum is valid

in practise, the file was never written unless the checksum
was valid, but in the same of sloccount reduction i made it
do the swap/copy before checking. while functionally ok, it
never sat right with me. this is one example of where sloc
count doesn't mean everything. code correctness is critical

Signed-off-by: Leah Rowe <leah@libreboot.org>

util/nvmutil/nvmutil.c

@@ -205,16 +205,18 @@ cmd_brick(void)
 void
 cmd_swap(void)
 {
-	xorswap(gbe[0], gbe[1]); /* speedhack: swap ptr, not words */
 	gbeFileModified = nvmPartModified[0] = nvmPartModified[1]
 	    = validChecksum(1) | validChecksum(0);
+	if (gbeFileModified)
+		xorswap(gbe[0], gbe[1]); /* speedhack: swap ptr, not words */
 }
 
 void
 cmd_copy(void)
 {
-	gbe[part ^ 1] = gbe[part]; /* speedhack: copy ptr, not words */
 	gbeFileModified = nvmPartModified[part ^ 1] = validChecksum(part);
+	if (gbeFileModified)
+		gbe[part ^ 1] = gbe[part]; /* speedhack: copy ptr, not words */
 }
 
 int