Don't warn if /dev was already mounted

This happens in syspart mode when CONFIG_DEVTMPFS_MOUNT=y.

Author: mthuurne

mininit.c

@@ -97,7 +97,7 @@ int main(int argc, char **argv, char **envp)
 	logfile = stderr;
 
 	/* Mount devtmpfs to get a full set of device nodes. */
-	if (mount("devtmpfs", "/dev", "devtmpfs", 0, NULL)) {
+	if (mount("devtmpfs", "/dev", "devtmpfs", 0, NULL) && errno != EBUSY) {
 		INFO("Couldn't mount devtmpfs on /dev: %d\n", errno);
 		/* If there are sufficient static device nodes in the fs containing
 		 * mininit, we can boot without devtmpfs, so don't give up yet. */