net: octeontx-83xx: Drop unused octeontx_fpavf_alloc_lock

The SDK commit 37c4a44a ("octeontx-83: domain based driver for
83xx") introduced an unused mutex. Drop it to fix the build warning.

Signed-off-by: Kevin Hao <kexin.hao@windriver.com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>