bpf, docs: Remove duplicated word "instructions"

The word "instructions" is duplicated, remove it.
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/1651139754-4838-2-git-send-email-yangtiezhu@loongson.cn

Documentation/bpf/instruction-set.rst

@@ -130,7 +130,7 @@ Byte swap instructions
 The byte swap instructions use an instruction class of ``BFP_ALU`` and a 4-bit
 code field of ``BPF_END``.
 
-The byte swap instructions instructions operate on the destination register
+The byte swap instructions operate on the destination register
 only and do not use a separate source register or immediate value.
 
 The 1-bit source operand field in the opcode is used to to select what byte