mvebu: remove bashism

"[[" is a bash extension for test. As the ash-implementation is not
fully compatible we drop its usage.

Signed-off-by: Sven Roederer <[email protected]>
[split patch, remove shebang, adjust commit title/message]
Signed-off-by: Adrian Schmutzler <[email protected]>

target/linux/mvebu/cortexa53/base-files/lib/upgrade/uDPU.sh

@@ -31,7 +31,7 @@ udpu_do_part_check() {
 
 	# Check if the block devices exist
 	for num in ${emmc_parts}; do
-		[[ ! -b ${emmc_dev}p${num} ]] && part_valid="0"
+		[ ! -b ${emmc_dev}p${num} ] && part_valid="0"
 	done
 
 	# If partitions are missing create a new partition table