mailbox: arm_mhuv3: Remove no_free_ptr() to maintain the original form of the pointer

Remove no_free_ptr() to ensure PTR_ERR() consistently retrieves the correct
error code.

Signed-off-by: Liao Yuanhong <liaoyuanhong@vivo.com>
Acked-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com>