net: cavium: remove unused lock octeontx_fpavf_alloc_lock

commit d38c2fb1

(octeontx-83: domain based driver for 83xx) defined
octeontx_fpavf_alloc_lock but not used in code, this will cause build
warning below, remove this mutex lock to fix.

drivers/net/ethernet/cavium/octeontx-83xx/fpavf_main.c:27:21: warning: 'octeontx_fpavf_alloc_lock' defined but not used [-Wunused-variable]
  27 | static DEFINE_MUTEX(octeontx_fpavf_alloc_lock);
     |                     ^~~~~~~~~~~~~~~~~~~~~~~~~

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