ethernet: ti: am65-cpts: Add missing inline qualifier to stub functions

When building with Clang:

In file included from drivers/net/ethernet/ti/am65-cpsw-ethtool.c:15:
drivers/net/ethernet/ti/am65-cpts.h:58:12: warning: unused function
'am65_cpts_ns_gettime' [-Wunused-function]
static s64 am65_cpts_ns_gettime(struct am65_cpts *cpts)
           ^
drivers/net/ethernet/ti/am65-cpts.h:63:12: warning: unused function
'am65_cpts_estf_enable' [-Wunused-function]
static int am65_cpts_estf_enable(struct am65_cpts *cpts,
           ^
drivers/net/ethernet/ti/am65-cpts.h:69:13: warning: unused function
'am65_cpts_estf_disable' [-Wunused-function]
static void am65_cpts_estf_disable(struct am65_cpts *cpts, int idx)
            ^
3 warnings generated.

These functions need to be marked as inline, which adds __maybe_unused,
to avoid these warnings, which is the pattern for stub functions.

Fixes: ec008fa2 ("ethernet: ti: am65-cpts: add routines to support taprio offload")
Link: https://github.com/ClangBuiltLinux/linux/issues/1026


Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>