riscv: Fix wrong usage of lm_alias() when splitting a huge linear mapping

lm_alias() can only be used on kernel mappings since it explicitly uses
__pa_symbol(), so simply fix this by checking where the address belongs
to before.

Fixes: 311cd2f6

 ("riscv: Fix set_memory_XX() and set_direct_map_XX() by splitting huge linear mappings")
Reported-by:  <syzbot+afb726d49f84c8d95ee1@syzkaller.appspotmail.com>
Closes: https://lore.kernel.org/linux-riscv/000000000000620dd0060c02c5e1@google.com/
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Reviewed-by: Charlie Jenkins <charlie@rivosinc.com>
Link: https://lore.kernel.org/r/20231212195400.128457-1-alexghiti@rivosinc.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>