Change CMSIS clone instructions from version 6 to 5

Updated instructions to clone CMSIS version 5 instead of 6, for improved backward compatibility.

Author: felipe-iar

NOTES.md

@@ -11,15 +11,15 @@ The recommended solution is to use `git` for fetching up-to-date CMSIS headers:
 * Linux (as root):
 ```
 cd /opt/iar/
-git clone https://github.com/arm-software/cmsis_6
+git clone https://github.com/arm-software/cmsis_5
 cd ewarm/arm
-ln -s ../../cmsis_6/CMSIS CMSIS
+ln -s ../../cmsis_5/CMSIS
 ```
 * Windows (Administrative Command Prompt):
 ```
 cd /iar/
-git clone https://github.com/arm-software/cmsis_6
+git clone https://github.com/arm-software/cmsis_5
 mklink -d ewarm-10.xx.x ewarm
 cd ewarm/arm
-mklink -d ../../cmsis_6/CMSIS CMSIS
+mklink -d ../../cmsis_5/CMSIS
 ```