bpf, x86: Use emit_nops to replace memcpy x86_nops

Move emit_nops() before emit_prologue() and replace
memcpy(prog, x86_nops[5], X86_PATCH_SIZE) with emit_nops(&prog, X86_PATCH_SIZE).

Signed-off-by: Leon Hwang <hffilwlqm@gmail.com>
Link: https://lore.kernel.org/r/20240104142226.87869-2-hffilwlqm@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>