board/freescale/mxs: fix Linux booting

Actually DTB_LIST accepts only file and not files with relative path
preprended. This leads to have vfat without .dtb files and so Linux
doesn't start. Let's fix this by including slash in sed command as done
for mxc as well as basename in front of $dt.dtb to remove possible
useless folders present in the dts path. Let's also add set -e at the
top of the script to make it more verbose on error and modify this
section according to spellcheck as done for mxc.

This commit align this "mxs/post-image.sh" with its "imx/post-image.sh"
counterpart which was improved for arm64 in commit [1].

[1] https://gitlab.com/buildroot.org/buildroot/-/commit/4755bf2bd43a7b4c3bf4f88be790240a01b3116f

Signed-off-by: Giulio Benetti <giulio.benetti@benettiengineering.com>
[Julien:
 - change space indentation to tabs for consistency
 - add note in commit log about imx/post-image.sh
]
Signed-off-by: Julien Olivain <ju.o@free.fr>

board/freescale/common/mxs/post-image.sh

@@ -1,5 +1,7 @@
 #!/usr/bin/env bash
 
+set -e
+
 #
 # dtb_list extracts the list of DTB files from BR2_LINUX_KERNEL_INTREE_DTS_NAME
 # in ${BR_CONFIG}, then prints the corresponding list of file names for the
@@ -7,10 +9,12 @@
 #
 dtb_list()
 {
-	local DTB_LIST="$(sed -n 's/^BR2_LINUX_KERNEL_INTREE_DTS_NAME="\([a-z0-9 \-]*\)"$/\1/p' ${BR2_CONFIG})"
+	local DTB_LIST
+
+	DTB_LIST="$(sed -n 's/^BR2_LINUX_KERNEL_INTREE_DTS_NAME="\([\/a-z0-9 \-]*\)"$/\1/p' "${BR2_CONFIG}")"
 
 	for dt in $DTB_LIST; do
-		echo -n "\"$dt.dtb\", "
+		echo -n "\"$(basename "${dt}").dtb\", "
 	done
 }