riscv: module: remove relocation_head rel_entry member allocation

relocation_head's list_head member, rel_entry, doesn't need to be
allocated, its storage can just be part of the allocated relocation_head.
Remove the pointer which allows to get rid of the allocation as well as
an existing memory leak found by Kai Zhang using kmemleak.

Fixes: 8fd6c514 ("riscv: Add remaining module relocations")
Reported-by: Kai Zhang <zhangkai@iscas.ac.cn>
Signed-off-by: Clément Léger <cleger@rivosinc.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Charlie Jenkins <charlie@rivosinc.com>
Tested-by: Charlie Jenkins <charlie@rivosinc.com>
Link: https://lore.kernel.org/r/20241128081636.3620468-1-cleger@rivosinc.com


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