riscv: module: Fix out-of-bounds relocation access

The current code allows rel[j] to access one element past the end of the
relocation section. Simplify to num_relocations which is equivalent to
the existing size expression.

Fixes: 080c4324 ("riscv: optimize ELF relocation function in riscv")
Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
Reviewed-by: Maxim Kochetkov <fido_max@inbox.ru>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20250409171526.862481-1-samuel.holland@sifive.com


Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>