octeontx2-af: Fix return value in rvu_mbox_handler_nix_lf_stop_rx

commit b87ecbb9c9ada88df50f77410c59379bb68b91a0 from
git@git.assembla.com:cavium/WindRiver.linux.git

The recent change to re-enable mac tx in nix_lf_stop_rx handler may
cause a problem because of the return value of function rvu_cgx_tx_enable,
which is called from this function. Fixed the issue by not returning the
return value of rvu_cgx_tx_enable.

Fixes: b58ece6ebd87 ("octeontx2-af: Re-enable mac tx in otx2_stop routine")
Change-Id: I9dcc544446cb30a9416bbfb32bd4773bd53d9e4a
Signed-off-by: Naveen Mamindlapalli <naveenm@marvell.com>
Reviewed-on: https://sj1git1.cavium.com/c/IP/SW/kernel/linux/+/86750
Tested-by: sa_ip-sw-jenkins <sa_ip-sw-jenkins@marvell.com>
Reviewed-by: Sunil Kovvuri Goutham <sgoutham@marvell.com>
(cherry picked from commit aee2df6b38b2bcf90ff6c270763ccf4fd9289a33)
Reviewed-on: https://sj1git1.cavium.com/c/IP/SW/kernel/linux/+/86854
Reviewed-on: https://sj1git1.cavium.com/c/IP/SW/kernel/linux/+/100340
Signed-off-by: Ruiqiang Hao <Ruiqiang.Hao@windriver.com>