MAINTAINERS: add a sub-entry for the Qualcomm bluetooth driver

Patches modifying drivers/bluetooth/hci_qca.c should be Cc'ed to the
linux-arm-msm mailing list so that Qualcomm maintainers and reviewers
can get notified about proposed changes to it. Add a sub-entry that adds
the mailing list to the list of addresses returned by get_maintainer.pl.

Acked-by: Konrad Dybcio <konradybcio@kernel.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>