crypto: octeontx2 - Remove the unneeded result variable

commit d43cbecd8f36a7e1067029196a03ba6f5f18386f from
git@git.assembla.com:cavium/WindRiver.linux.git

Return the value otx2_cpt_send_mbox_msg() directly instead of storing it
in another redundant variable.

Reported-by: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: ye xingchen <ye.xingchen@zte.com.cn>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Change-Id: I7a73ae0f17b53ee90ff818da7eb6b02c84f5280c
Reviewed-on: https://sj1git1.cavium.com/c/IP/SW/kernel/linux/+/90414


Tested-by: sa_ip-sw-jenkins <sa_ip-sw-jenkins@marvell.com>
Reviewed-by: Nithin Kumar Dabilpuram <ndabilpuram@marvell.com>
Reviewed-by: Sunil Kovvuri Goutham <sgoutham@marvell.com>
Signed-off-by: Wenlin Kang <wenlin.kang@windriver.com>