trusted-firmware-a.mk: use correct CPE ID

trusted-firmware-a.mk: use correct CPE ID

There are 2 different CPE IDs on the NVD website:
cpe:/a:arm:trusted_firmware-a
cpe:/o:arm:arm_trusted_firmware

The ID as currently used in trusted-firmware-a.mk does not exist. The
CPE ID using the arm_trusted_firmware product name only lists a few
records for versions 2.2 and 2.3 on the NVD site. The CPE ID using the
trusted_firmware-a product name lists many more records, and actually
has a CVE linked to it. Therefore, use the CPE ID using the
trusted_firmware-a product name.

Fixes: 104d60fe94ce ("trusted-firmware-a.mk: add PKG_CPE_ID")
Signed-off-by: Stijn Tintel <stijn@linux-ipv6.be>