ath79: fix position of SPDX license identifier

Strictly, the identifier needs to be in the line directly after the
shebang.

Signed-off-by: Adrian Schmutzler <[email protected]>

target/linux/ath79/nand/base-files/etc/init.d/bootcount

@@ -1,5 +1,4 @@
 #!/bin/sh /etc/rc.common
-
 # SPDX-License-Identifier: GPL-2.0-only
 
 START=99