soc: mediatek: svs: Fix memory leak in svs_enable_debug_write()

soc: mediatek: svs: Fix memory leak in svs_enable_debug_write()

In svs_enable_debug_write(), the buf allocated by memdup_user_nul()
is leaked if kstrtoint() fails.

Fix this by using __free(kfree) to automatically free buf, eliminating
the need for explicit kfree() calls and preventing leaks.

Fixes: 13f1bbcfb582 ("soc: mediatek: SVS: add debug commands")
Co-developed-by: Jianhao Xu <jianhao.xu@seu.edu.cn>
Signed-off-by: Jianhao Xu <jianhao.xu@seu.edu.cn>
Signed-off-by: Zilin Guan <zilin@seu.edu.cn>
[Angelo: Added missing cleanup.h inclusion]
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>