rpmsg: slatecom: Discard unaligned packet to read

If intent_alloc_size and chunk size are unaligned with the minimum offset,
then ahb_read can lead to bytes overflow as ahb_read is performed
with word_size aligned.

If the received chunk_size is not aligned to word_size, discard packet
to read.

Change-Id: Iae2c87636675da653bd182ac082a285b699e0a83
Signed-off-by: Kaushal Hooda <quic_khooda@quicinc.com>