tools: iot2050-sign-fw.sh: Make localization of tools dir more robust

When building in-tree, there is no source link.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
diff --git a/tools/iot2050-sign-fw.sh b/tools/iot2050-sign-fw.sh
index 6b426c8..75ffd56 100755
--- a/tools/iot2050-sign-fw.sh
+++ b/tools/iot2050-sign-fw.sh
@@ -5,6 +5,8 @@
 	exit 1
 fi
 
+TOOLS_DIR=$(dirname $0)
+
 TEMP_X509=$(mktemp XXXXXXXX.temp)
 
 REVISION=${2:-0}
@@ -39,10 +41,10 @@
 
 openssl req -new -x509 -key $1 -nodes -outform DER -out $CERT_X509 -config $TEMP_X509 -sha512
 cat $CERT_X509 tispl.bin > tispl.bin_signed
-source/tools/binman/binman replace -i flash-pg1.bin -f tispl.bin_signed fit@180000
-source/tools/binman/binman replace -i flash-pg2.bin -f tispl.bin_signed fit@180000
+$TOOLS_DIR/binman/binman replace -i flash-pg1.bin -f tispl.bin_signed fit@180000
+$TOOLS_DIR/binman/binman replace -i flash-pg2.bin -f tispl.bin_signed fit@180000
 
 rm $TEMP_X509 $CERT_X509
 
-source/tools/binman/binman sign -i flash-pg1.bin -k $1 -a sha256,rsa4096 fit@380000
-source/tools/binman/binman sign -i flash-pg2.bin -k $1 -a sha256,rsa4096 fit@380000
+$TOOLS_DIR/binman/binman sign -i flash-pg1.bin -k $1 -a sha256,rsa4096 fit@380000
+$TOOLS_DIR/binman/binman sign -i flash-pg2.bin -k $1 -a sha256,rsa4096 fit@380000