riscv, bpf: use lw when reading int cpu in bpf_get_smp_processor_id

riscv, bpf: use lw when reading int cpu in bpf_get_smp_processor_id

emit_ld is wrong, because thread_info.cpu is 32-bit, not xlen-bit wide.
The struct currently has a hole after cpu, so little endian accesses
seemed fine.

Fixes: 2ddec2c80b44 ("riscv, bpf: inline bpf_get_smp_processor_id()")
Cc: stable@vger.kernel.org
Signed-off-by: Radim Krčmář <rkrcmar@ventanamicro.com>
Reviewed-by: Pu Lehui <pulehui@huawei.com>
Link: https://lore.kernel.org/r/20250812090256.757273-4-rkrcmar@ventanamicro.com
Signed-off-by: Paul Walmsley <pjw@kernel.org>