board/terasic/de10nano_cyclone5: disable shellcheck SC2276

Disable shellcheck SC2276 warning introduced in v0.7.2 [1]
for barebox environment file.

[1] https://github.com/koalaman/shellcheck/commit/fbb14d6b384a65ee16781966d9d240db9ed7b644

Signed-off-by: Romain Naour <romain.naour@smile.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

board/terasic/de10nano_cyclone5/barebox-env/boot/mmc

@@ -1,5 +1,6 @@
 #!/bin/sh
 
+# shellcheck disable=SC2276
 global.bootm.oftree="/boot/socfpga_cyclone5_de0_nano_soc.dtb"
 global.bootm.image="/boot/zImage"