fvp: fix compiler warning
fvp: fix compiler warning

Fixes compiler warning when compiling with default
CFG_TEE_CORE_LOG_LEVEL.

pascal-brand-st-dev/optee_os,Microsoft/optee_os,matt2048/optee_os,chshxi1989/optee_os,Microsoft/optee_os,BreezeWu/optee_os,pascal-brand-st-dev/optee_os,chshxi1989/optee_os,jamescfkung/optee_os,jamescfkung/optee_os,pascal-brand-st-dev/optee_os,cedric-chaumont-st-dev/optee_os,BreezeWu/optee_os,jamescfkung/optee_os,matt2048/optee_os,cedric-chaumont-st-dev/optee_os,cedric-chaumont-st-dev/optee_os,matt2048/optee_os,pascal-brand-st-dev/optee_os,chshxi1989/optee_os,BreezeWu/optee_os,Microsoft/optee_os,chshxi1989/optee_os,cedric-chaumont-st-dev/optee_os,matt2048/optee_os,Microsoft/optee_os,jamescfkung/optee_os,Microsoft/optee_os,pascal-brand-st-dev/optee_os,jamescfkung/optee_os,BreezeWu/optee_os,BreezeWu/optee_os,chshxi1989/optee_os