files/toolchain-shar-template.sh: fix replace target_sdk_dir twice in environment setup file

When specify a target sdk dir that contains default install dir as
subdir,

	target_sdk_dir=/opt/poky/$version/
	custom_target_sdk_dir=/opt/poky/$version/some

The target_sdk_dir variable in environment-setup file is replaced twice
causes to point to wrong PATH.

In order to fix filter environment-setup file in second replacement.

[YOCTO #7032]

Signed-off-by: Aníbal Limón <anibal.limon@linux.intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>