riscv: Correctly free relocation hashtable on error

When there is not enough allocatable memory for the relocation
hashtable, module loading should exit gracefully. Previously, this was
attempted to be accomplished by checking if an unsigned number is less
than zero which does not work. Instead have the caller check if the
hashtable was correctly allocated and add a comment explaining that
hashtable_bits that is 0 is valid.

Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
Fixes: d8792a57 ("riscv: Safely remove entries from relocation list")
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/r/202312132019.iYGTwW0L-lkp@intel.com/


Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Julia Lawall <julia.lawall@inria.fr>
Closes: https://lore.kernel.org/r/202312120044.wTI1Uyaa-lkp@intel.com/


Reviewed-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://lore.kernel.org/r/20240104-module_loading_fix-v3-2-a71f8de6ce0f@rivosinc.com


Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>