wifi: rtw89: debug: Fix memory leak in __print_txpwr_map()

wifi: rtw89: debug: Fix memory leak in __print_txpwr_map()

In __print_txpwr_map(), memory is allocated to bufp via vzalloc().
If max_valid_addr is 0, the function returns -EOPNOTSUPP immediately
without freeing bufp, leading to a memory leak.

Since the validation of max_valid_addr does not depend on the allocated
memory, fix this by moving the vzalloc() call after the check.

Compile tested only. Issue found using a prototype static analysis tool
and code review.

Fixes: 036042e15770 ("wifi: rtw89: debug: txpwr table supports Wi-Fi 7 chips")
Suggested-by: Zong-Zhe Yang <kevin_yang@realtek.com>
Signed-off-by: Zilin Guan <zilin@seu.edu.cn>
Reviewed-by: Zong-Zhe Yang <kevin_yang@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://patch.msgid.link/20260116130834.1413924-1-zilin@seu.edu.cn