drivers: tee: optee: fix possible null pointer dereference

Add check for supp->current being NULL before accessing num_params in
error log.

Prevent potential NULL pointer dereference and crash when invalid
parameter count

Improve error messages for better debugging in cases with no current
request or wrong param count.

Signed-off-by: Gaetan Perrot <gaetan.perrot@spacecubics.com>