vppinfra: fix clang-10 build error with asm inline
vppinfra: fix clang-10 build error with asm inline

clang start to support parse asm inline from clang-11,
Use asm volatile instead.

Type: fix
Fixes: d5045e68a782 ("vppinfra: introduce clib_perfmom")
Signed-off-by: Tianyu Li <1c599f4cedabb0c78bbfcbf824f5988c7b6a2be4@arm.com>
Change-Id: I00e5e19856caaed94e22f8fa6cf4f918483976a4

chrisy/vpp,FDio/vpp,FDio/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp