regmap: include linux/sched.h to fix build

This fixes:

drivers/base/regmap/regmap.c: In function 'regmap_async_complete_cb':
drivers/base/regmap/regmap.c:1656:3: error: 'TASK_NORMAL' undeclared (first use in this function)
drivers/base/regmap/regmap.c:1656:3: note: each undeclared identifier is reported only once for each function it appears in
drivers/base/regmap/regmap.c: In function 'regmap_async_complete':
drivers/base/regmap/regmap.c:1688:2: error: 'TASK_UNINTERRUPTIBLE' undeclared (first use in this function)
drivers/base/regmap/regmap.c:1688:2: error: implicit declaration of function 'schedule'

An alternative might be to adjust linux/wait.h to include linux/sched.h,
but since that hasn't been done before, I assume we're consciously
avoiding doing that.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

drivers/base/regmap/regmap.c

@@ -16,6 +16,7 @@
 #include <linux/mutex.h>
 #include <linux/err.h>
 #include <linux/rbtree.h>
+#include <linux/sched.h>
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/regmap.h>