target/loongarch: Remove target_ulong use in gdb_write_register handler

target/loongarch: Remove target_ulong use in gdb_write_register handler

ldq_le_p() returns a uint64_t type, big enough to also hold
ldl_le_p() return value. If we were building for a 32-bit
LoongArch target, ldq_le_p() would not fit in target_ulong.
Better stick to plain uint64_t.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Song Gao <gaosong@loongson.cn>
Message-Id: <20251009201947.34643-4-philmd@linaro.org>