This include was needed to suppress build error when this driver
was initially merged because <linux/regmap.h> did not include
<linux/delay.h> at that time.  (developers' headache across
sub-systems)

The root cause has been fixed by commit adf08d48 ("regmap:
include <linux/delay.h> from include/linux/regmap.h"), so this
line can be dropped now.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>