riscv: misaligned: use get_user() instead of __get_user()

riscv: misaligned: use get_user() instead of __get_user()

Now that we can safely handle user memory accesses while in the
misaligned access handlers, use get_user() instead of __get_user() to
have user memory access checks.

Signed-off-by: Clément Léger <cleger@rivosinc.com>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20250422162324.956065-4-cleger@rivosinc.com
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>