riscv: uaccess: use 'asm_goto_output' for get_user()

riscv: uaccess: use 'asm_goto_output' for get_user()

With 'asm goto' we don't need to test the error etc, the exception just
jumps to the error handling directly.

Unlike put_user(), get_user() must work around GCC bugs [1] when using
output clobbers in an asm goto statement.

Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113921
Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
[Cyril Bur: Rewritten commit message]
Signed-off-by: Cyril Bur <cyrilbur@tenstorrent.com>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20250410070526.3160847-6-cyrilbur@tenstorrent.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>