LoongArch: Fix hw_breakpoint_control() for watchpoints

In hw_breakpoint_control(), encode_ctrl_reg() has already encoded the
MWPnCFG3_LoadEn/MWPnCFG3_StoreEn bits in info->ctrl. We don't need to
add (1 << MWPnCFG3_LoadEn | 1 << MWPnCFG3_StoreEn) unconditionally.

Otherwise we can't set read watchpoint and write watchpoint separately.

Cc: stable@vger.kernel.org
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>