Makefile.am: update clang-format command

Use grep -E instead of egrep

Signed-off-by: Sohan Kunkerkar <sohank2602@gmail.com>

Makefile.am

@@ -275,7 +275,7 @@ generate-mount_flags.c: src/libcrun/mount_flags.perf
 
 clang-format:
 # do not format files that were copied into the source directory.
-	git ls-files src tests | egrep "\\.[hc]" | grep -v "chroot_realpath.c\|cloned_binary.c\|signals.c\|mount_flags.c" | xargs clang-format -style=file -i
+	git ls-files src tests | grep -E "\\.[hc]" | grep -v "chroot_realpath.c\|cloned_binary.c\|signals.c\|mount_flags.c" | xargs clang-format -style=file -i
 
 shellcheck:
 	shellcheck tests/*/*.sh contrib/*.sh