bus: mhi: host: Add alignment check for event ring read pointer

In the Linux kernel, the following vulnerability has been resolved:

bus: mhi: host: Add alignment check for event ring read pointer

Though we do check the event ring read pointer by "is_valid_ring_ptr"

to make sure it is in the buffer range, but there is another risk the

pointer may be not aligned. Since we are expecting event ring elements

are 128 bits(struct mhi_ring_element) aligned, an unaligned read pointer

could lead to multiple issues like DoS or ring buffer memory corruption.

So add a alignment check for event ring read pointer.