clk: s2mps11: Add used attribute to s2mps11_dt_match

Clang warns after commit 8985167ecf ("clk: s2mps11: Fix matching when
built as module and DT node contains compatible"):

drivers/clk/clk-s2mps11.c:242:34: warning: variable 's2mps11_dt_match'
is not needed and will not be emitted [-Wunneeded-internal-declaration]
static const struct of_device_id s2mps11_dt_match[] = {
                                 ^
1 warning generated.

This warning happens when a variable is used in some construct that
doesn't require a reference to that variable to be emitted in the symbol
table; in this case, it's MODULE_DEVICE_TABLE, which only needs to hold
the data of the variable, not the variable itself.

$ nm -S drivers/clk/clk-s2mps11.o | rg s2mps11_dt_match
00000078 000003d4 R __mod_of__s2mps11_dt_match_device_table

Normally, with device ID table variables, it means that the variable
just needs to be tied to the device declaration at the bottom of the
file, like s2mps11_clk_id:

$ nm -S drivers/clk/clk-s2mps11.o | rg s2mps11_clk_id
00000000 00000078 R __mod_platform__s2mps11_clk_id_device_table
00000000 00000078 r s2mps11_clk_id

However, because the comment above this deliberately doesn't want this
variable added to .of_match_table, we need to mark s2mps11_dt_match as
__used to silence this warning. This makes it clear to Clang that the
variable is used for something, even if a reference to it isn't being
emitted.

Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Fixes: 8985167ecf ("clk: s2mps11: Fix matching when built as module and DT node contains compatible")
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

drivers/clk/clk-s2mps11.c

@@ -255,7 +255,7 @@ MODULE_DEVICE_TABLE(platform, s2mps11_clk_id);
  * This requires of_device_id table.  In the same time this will not change the
  * actual *device* matching so do not add .of_match_table.
  */
-static const struct of_device_id s2mps11_dt_match[] = {
+static const struct of_device_id s2mps11_dt_match[] __used = {
 	{
 		.compatible = "samsung,s2mps11-clk",
 		.data = (void *)S2MPS11X,