Clarify a comment in dmi_memory_device_extended_size

Improve the comment to avoid the confusion as reported in bug #48723:
http://savannah.nongnu.org/bugs/?48723

Author: jdelvare

dmidecode.c

@@ -2277,7 +2277,10 @@ static void dmi_memory_device_extended_size(u32 code)
 {
 	code &= 0x7FFFFFFFUL;
 
-	/* Use the most suitable unit depending on size */
+	/*
+	 * Use the greatest unit for which the exact value can be displayed
+	 * as an integer without rounding
+	 */
 	if (code & 0x3FFUL)
 		printf(" %lu MB", (unsigned long)code);
 	else if (code & 0xFFFFFUL)