rpmsg: glink: smem: Support rx peak for size less than 4 bytes

commit 928002a5e9dab2ddc1a0fe3e00739e89be30dc6b upstream.

The current rx peak function fails to read the data if size is
less than 4bytes.

Use memcpy_fromio to support data reads of size less than 4 bytes.

Cc: stable@vger.kernel.org
Fixes: f0beb4ba9b18 ("rpmsg: glink: Remove chunk size word align warning")
Signed-off-by: Arun Kumar Neelakantam <aneela@codeaurora.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Cc: nobuhiro1.iwamatsu@toshiba.co.jp
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>