Bluetooth: btmtk: Fix short read errors in btmtk_usb_reg_read()

Bluetooth: btmtk: Fix short read errors in btmtk_usb_reg_read()

If btmtk_usb_reg_read() gets a "short" read from a device, it will
accidentally treat that as a "real" read and populate the returned value
with some unknown and probably totally invalid data.

Fix this logic error up by calling usb_control_msg_recv() which
guarantees a "full" read happens, and then simplify the error checking
for when btmtk_usb_reg_read() is called (it's really just
btmtk_usb_id_get() that calls btmtk_usb_reg_read(), so fix up those
return sites.

Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>