tools: imx8mimage: not abort when mmap fail

When creating flash.bin, the hdmi firmware might not be
copied to U-Boot source tree. Then mkimage will fail.
However we are switching to binman, binman will show the
message if the file not there, and create empty file per
i.MX8MQ binman node. So we not fail mkimage here othersize
CI will fail if hdmi firmware not copied here.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
diff --git a/tools/imx8mimage.c b/tools/imx8mimage.c
index 11e40cc..4eed683 100644
--- a/tools/imx8mimage.c
+++ b/tools/imx8mimage.c
@@ -271,7 +271,7 @@
 	if (ptr == MAP_FAILED) {
 		fprintf(stderr, "Can't read %s: %s\n",
 			datafile, strerror(errno));
-		exit(EXIT_FAILURE);
+		goto err_mmap;
 	}
 
 	size = sbuf.st_size - datafile_offset;
@@ -311,6 +311,7 @@
 	}
 
 	munmap((void *)ptr, sbuf.st_size);
+err_mmap:
 	close(dfd);
 }