RSS: remove hard check of 4 bytes alignment of MHUv3 buffer

For mhu_v3 transfer there is no hard requirement of 4 Byte alignment of
buffer size. This patch removes the 4 Bytes conditional check for buffer
size alignment.

Signed-off-by: Sayanta Pattanayak <sayanta.pattanayak@arm.com>
Change-Id: I370e0f4eefa4f03b4baffa39b39f07ab2bab1886