ui/devcmd: make sure the 'total size' argument for the 'erase' command makes sense

ui/devcmd.c

@@ -207,6 +207,12 @@ int cmd_erase(char **arg)
 					   "0x%x\n", segment_size);
 				return -1;
 			}
+
+			if (total_size % segment_size != 0) {
+				printc_err("erase: total size must be a multiple of the "
+				           "segment size!\n");
+				return -1;
+			}
 		} else {
 			printc_err("erase: unknown erase type: %s\n",
 				    type_text);