riscv: Avoid unaligned access when relocating modules

With the C-extension regular 32bit instructions are not
necessarily aligned on 4-byte boundaries. RISC-V instructions
are in fact an ordered list of 16bit little-endian
"parcels", so access the instruction as such.

This should also make the code work in case someone builds
a big-endian RISC-V machine.
Signed-off-by: Emil Renner Berthing <kernel@esmil.dk>
Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
Link: https://lore.kernel.org/r/20231101-module_relocations-v9-1-8dfa3483c400@rivosinc.comSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>