riscv: mm: init: remove unnecessary "#ifdef CONFIG_CRASH_DUMP"

The is_kdump_kernel() returns false for !CRASH_DUMP case, so we don't
need the #ifdef CONFIG_CRASH_DUMP for is_kdump_kernel() checking.

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Reviewed-by: Alexandre Ghiti <alex@ghiti.fr>
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>