MAINTAINERS: add drivers/pinctrl/qcom to ARM/QUALCOMM SUPPORT

When running checkpatch.pl on a new pinctrl driver in
drivers/pinctrl/qcom, I noticed a warning about creating
a new maintainer.  The drivers/pinctrl/qcom folder doesn't have
anyone assigned in the MAINTAINERS file.

Let's assign it to ARM/QUALCOMM SUPPORT.

Signed-off-by: Michael Scott <michael.scott@linaro.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>