util/nvmutil: cleaner directory checking

opendir allocates resources and causes a bunch of other
error conditions which we need to catch.

use of stat is more efficient here.

Signed-off-by: Leah Rowe <leah@libreboot.org>

util/nvmutil/nvmutil.c

@@ -138,16 +138,6 @@ set_io_flags(int argc, char *argv[])
 			flags = O_RDONLY;
 }
 
-void
-checkdir(const char *path)
-{
-	if (opendir(path) != NULL)
-		err(set_err(EISDIR), "%s", path);
-	if (errno == ENOTDIR)
-		errno = 0;
-	err_if(errno);
-}
-
 void
 openFiles(void)
 {
@@ -171,6 +161,18 @@ openFiles(void)
 	}
 }
 
+void
+checkdir(const char *path)
+{
+	struct stat st;
+	err_if (stat(path, &st) == -1);
+	if (S_ISDIR(st.st_mode))
+		err(set_err(EISDIR), "%s", path);
+	if (errno == ENOTDIR)
+		errno = 0;
+	err_if(errno);
+}
+
 void
 xopen(int *f, const char *l, int p, struct stat *st)
 {