board/stmicroelectronics: generalise BR2_TARGET_ARM_TRUSTED_FIRMWARE_ADDITIONAL_VARIABLES regex

The regex was a bit too strict in which characters it allowed. Thus,
if e.g. a file name appears in the
BR2_TARGET_ARM_TRUSTED_FIRMWARE_ADDITIONAL_VARIABLES string, it no
longer matches, and we end up with an empty ATF_VARIABLES. This makes
the subsequent grep fail, and the post-image.sh script fails without
any error message (thanks to the -e option).

Simplify the regex to match everything except the closing quotation
mark. Note that Kconfig doesn't allow quotation marks at all inside a
string (even escaped ones), so this regular expression is always OK.

Signed-off-by: Marleen Vos <marleen.vos@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

board/stmicroelectronics/common/stm32mp157/post-image.sh

@@ -8,7 +8,7 @@
 #
 atf_image()
 {
-	ATF_VARIABLES="$(sed -n 's/^BR2_TARGET_ARM_TRUSTED_FIRMWARE_ADDITIONAL_VARIABLES="\([\/a-zA-Z0-9_=. \-]*\)"$/\1/p' ${BR2_CONFIG})"
+	ATF_VARIABLES="$(sed -n 's/^BR2_TARGET_ARM_TRUSTED_FIRMWARE_ADDITIONAL_VARIABLES="\([^\"]*\)"$/\1/p' ${BR2_CONFIG})"
 	# make sure DTB_FILE_NAME is set
 	printf '%s\n' "${ATF_VARIABLES}" | grep -Eq 'DTB_FILE_NAME=[0-9A-Za-z_\-]*'
 	# extract the value