Rename tfm_target_name for ARM_MUSCA_B1

The mbed-os-tf-m-regression-tests build scripts gets a mapping of
Mbed OS target names to TF-M target names from `targets.json`. TF-M
v1.3 has renamed musca_b1 to musca_b1/sse_200, this commit updates
that accordingly to ensure successful build of TF-M and tests for
ARM_MUSCA_B1.

Author: LDong-Arm

targets/targets.json

@@ -4874,7 +4874,7 @@
             "function": "ArmMuscaB1Code.binary_hook"
         },
         "secure_image_filename": "tfm_s.bin",
-        "tfm_target_name": "musca_b1",
+        "tfm_target_name": "musca_b1/sse_200",
         "tfm_bootloader_supported": true,
         "tfm_default_toolchain": "ARMCLANG",
         "tfm_supported_toolchains": [