staging: ion: Fix error handling in ion_buffer_create

This patch fixes error handling case when buffer->pages allocation
fails. Also, it removes unreachable code of checking ret variable
although it is not updated.

Signed-off-by: Rohit kumar <rohit.kr@samsung.com>
Reviewed-by: Laura Abbott <labbott@redhat.com>
Suggested-by: Pintu Kumar <pintu.k@samsung.com>
Reviewed-by: Pintu Kumar <pintu.k@samsung.com>
Reviewed-by: Gioh Kim <gioh.kim@lge.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>