core: user_ta: set freed EXIDX pointer to NULL
core: user_ta: set freed EXIDX pointer to NULL

Clear reference of user TA exception index table once it
is freed, otherwise it is freed a second time. This
issue occurs when set_exidx() fails for some reasons as
an out of memory issue. This change prevents core from
panicking when it occurs.

Signed-off-by: Etienne Carriere <f21bc5b8f3ea1962eb45af359f1abea6578cab94@linaro.org>
Reviewed-by: Jerome Forissier <ced78d268b4c9a0a20a59a9feeebd2ad90da03d3@linaro.org>

pascal-brand-st-dev/optee_os,pascal-brand-st-dev/optee_os,pascal-brand-st-dev/optee_os,pascal-brand-st-dev/optee_os,pascal-brand-st-dev/optee_os