cache: sifive_ccache: Silence unused variable warning

With W=1 and CONFIG_RISCV_NONSTANDARD_CACHE_OPS=n, GCC warns:

drivers/cache/sifive_ccache.c: In function 'sifive_ccache_init':
drivers/cache/sifive_ccache.c:293:23: warning: variable 'quirks' set but not used [-Wunused-but-set-variable]
  293 |         unsigned long quirks;
      |                       ^~~~~~

This is expected, since QUIRK_NONSTANDARD_CACHE_OPS is the only quirk
still handled in this function.

Fixes: c90847b ("cache: sifive_ccache: Partially convert to a platform driver")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202403311253.Z4NvIBxI-lkp@intel.com/
Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>

Author: SiFiveHolland

drivers/cache/sifive_ccache.c

@@ -290,7 +290,7 @@ static int __init sifive_ccache_init(void)
 	struct device_node *np;
 	struct resource res;
 	const struct of_device_id *match;
-	unsigned long quirks;
+	unsigned long quirks __maybe_unused;
 	int rc;
 
 	np = of_find_matching_node_and_match(NULL, sifive_ccache_ids, &match);