dca: make function dca_common_get_tag static

Function dca_common_get_tag is local to the source and does not need to be
in global scope, so make it static.

Cleans up sparse warning:
drivers/dca/dca-core.c:273:4: warning: symbol 'dca_common_get_tag' was
not declared. Should it be static?

Signed-off-by: Colin Ian King <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/dca/dca-core.c

···
  * @dev - the device that wants dca service
  * @cpu - the cpuid as returned by get_cpu()
  */
-u8 dca_common_get_tag(struct device *dev, int cpu)
+static u8 dca_common_get_tag(struct device *dev, int cpu)
 {
 	struct dca_provider *dca;
 	u8 tag;