MLK-20239-7 imx8qm/qxp: Fix coverity CID 3303250

Fix coverity issue CID 3303250: Untrusted array index read (TAINTED_SCALAR)
tainted_data: Using tainted variable header.num_images - 1 as an index
into an array header.img
Signed-off-by: Ye Li <ye.li@nxp.com>

src/imx8qxb0.c

@@ -518,8 +518,10 @@ int get_container_image_start_pos(image_t *image_stack, uint32_t align)
 				break;
 			}
 
-			if(read(ofd, &header, sizeof(header)) != sizeof(header))
+			if(read(ofd, &header, sizeof(header)) != sizeof(header)) {
 				printf("Failure Read header \n");
+				exit(EXIT_FAILURE);
+			}
 
 			close(ofd);