MAINTAINERS: Use 'area: CMSIS API Layer' label

This commit updates the 'CMSIS API layer' entry to use the 'area: CMSIS
API Layer' label.

Signed-off-by: Stephanos Ioannidis <[email protected]>

Author: stephanosio

MAINTAINERS.yml

@@ -307,6 +307,7 @@ CMSIS API layer:
          - samples/subsys/portability/cmsis_rtos_v*/
          - tests/subsys/portability/cmsis_rtos_v*/
     labels:
+        - "area: CMSIS API Layer"
         - "area: Portability"
 
 CMSIS-DSP integration: