MAINTAINERS: update qtnfmac maintainers

I am leaving Quantenna, so I will no longer have access to firmware and
hardware. Meanwhile I plan to participate in reviewing qtnfmac patches
for a while until my firmware knowledge becomes completely obsolete.
Adding myself as a reviewer using my personal email address.
Signed-off-by: Sergey Matyukevich <sergey.matyukevich.os@quantenna.com>
Signed-off-by: Igor Mitsyanko <igor.mitsyanko.os@quantenna.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200520130800.1902-1-sergey.matyukevich.os@quantenna.com

MAINTAINERS

@@ -14066,7 +14066,7 @@ F:	drivers/net/wireless/ath/wcn36xx/
 
 QUANTENNA QTNFMAC WIRELESS DRIVER
 M:	Igor Mitsyanko <imitsyanko@quantenna.com>
-M:	Sergey Matyukevich <smatyukevich@quantenna.com>
+R:	Sergey Matyukevich <geomatsi@gmail.com>
 L:	linux-wireless@vger.kernel.org
 S:	Maintained
 F:	drivers/net/wireless/quantenna