cifsd: use kfree to free memory allocated by kmalloc or kzalloc

kfree should be used to free memory allocated by kmalloc or kzalloc to
avoid any overhead and for maintaining consistency.

Signed-off-by: Muhammad Usama Anjum <musamaanjum@gmail.com>
Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Steve French <stfrench@microsoft.com>