bpf, docs: fix BPF_NEG entry in instruction-set.rst

This patch fixes the documentation of the BPF_NEG instruction to
denote that it does not use the source register operand.

Signed-off-by: Jose E. Marchesi <jose.marchesi@oracle.com>
Acked-by: Dave Thaler <dthaler@microsoft.com>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20230726092543.6362-1-jose.marchesi@oracle.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: jemarch

Documentation/bpf/standardization/instruction-set.rst

@@ -165,7 +165,7 @@ BPF_OR    0x40   dst \|= src
 BPF_AND   0x50   dst &= src
 BPF_LSH   0x60   dst <<= (src & mask)
 BPF_RSH   0x70   dst >>= (src & mask)
-BPF_NEG   0x80   dst = -src
+BPF_NEG   0x80   dst = -dst
 BPF_MOD   0x90   dst = (src != 0) ? (dst % src) : dst
 BPF_XOR   0xa0   dst ^= src
 BPF_MOV   0xb0   dst = src