crypto: lib/mpi - Fix unexpected pointer access in mpi_ec_init

In the Linux kernel, the following vulnerability has been resolved: crypto: lib/mpi - Fix unexpected pointer access in mpi_ec_init When the mpi_ec_ctx structure is initialized, some fields are not cleared, causing a crash when referencing the field when the structure was released. Initially, this issue was ignored because memory for mpi_ec_ctx is allocated with the __GFP_ZERO flag. For example, this error will be triggered when calculating the Za value for SM2 separately.