hwrng: optee: Initialize some structs using memset instead of braces

Clang warns:

drivers/char/hw_random/optee-rng.c:80:31: warning: suggest braces around
initialization of subobject [-Wmissing-braces]
        struct tee_param param[4] = {0};
                                     ^
                                     {}
drivers/char/hw_random/optee-rng.c:177:31: warning: suggest braces
around initialization of subobject [-Wmissing-braces]
        struct tee_param param[4] = {0};
                                     ^
                                     {}
drivers/char/hw_random/optee-rng.c:212:48: warning: suggest braces
around initialization of subobject [-Wmissing-braces]
        struct tee_ioctl_open_session_arg sess_arg = {0};
                                                      ^
                                                      {}
3 warnings generated.

One way to fix these warnings is to add additional braces like Clang
suggests; however, there has been a bit of push back from some
maintainers, who just prefer memset as it is unambiguous, doesn't
depend on a particular compiler version, and properly initializes all
subobjects [1][2]. Do that here so there are no more warnings.

[1]: https://lore.kernel.org/lkml/022e41c0-8465-dc7a-a45c-64187ecd9684@amd.com/
[2]: https://lore.kernel.org/lkml/20181128.215241.702406654469517539.davem@davemloft.net/

Fixes: 5fe8b1cc ("hwrng: add OP-TEE based rng driver")
Link: https://github.com/ClangBuiltLinux/linux/issues/369


Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Reviewed-by: Sumit Garg <sumit.garg@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>