MAINTAINERS: fix broken doc refs due to yaml conversion

Several *.txt files got converted to yaml. Update their
references at MAINTAINERS file accordingly.

Signed-off-by: Mauro Carvalho Chehab <[e-mail]>
Acked-by: Stephen Boyd <[e-mail]>
Link: https://lore.kernel.org/r/3b58af[e-mail]
Signed-off-by: Jonathan Corbet <[e-mail]>

Documentation/devicetree/bindings/clock/hi6220-clock.txt

···
 please refer the following document to know more about the binding rules
 for these system controllers:
 
-Documentation/devicetree/bindings/arm/hisilicon/hisilicon.txt
+Documentation/devicetree/bindings/arm/hisilicon/hisilicon.yaml
 
 Required Properties:
 

MAINTAINERS

···
 L:	[e-mail]
 S:	Supported
 W:	http://ez.analog.com/community/linux-device-drivers
-F:	Documentation/devicetree/bindings/iio/adc/adi,ad7768-1.txt
+F:	Documentation/devicetree/bindings/iio/adc/adi,ad7768-1.yaml
 F:	drivers/iio/adc/ad7768-1.c
 
 ANALOG DEVICES INC AD7780 DRIVER
···
 L:	[e-mail]
 S:	Maintained
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/peter.chen/usb.git
-F:	Documentation/devicetree/bindings/usb/cdns-usb3.txt
+F:	Documentation/devicetree/bindings/usb/cdns,usb3.yaml
 F:	drivers/usb/cdns3/
 
 CADET FM/AM RADIO RECEIVER DRIVER
···
 M:	[e-mail]
 S:	Maintained
 W:	http://www.hisilicon.com
-F:	Documentation/devicetree/bindings/arm/hisilicon/hisilicon-low-pin-count.txt
+F:	Documentation/devicetree/bindings/arm/hisilicon/low-pin-count.yaml
 F:	drivers/bus/hisi_lpc.c
 
 HISILICON NETWORK SUBSYSTEM 3 DRIVER (HNS3)
···
 R:	Sergei Shtylyov <[e-mail]>
 L:	[e-mail]
 L:	[e-mail]
-F:	Documentation/devicetree/bindings/net/renesas,*.txt
 F:	Documentation/devicetree/bindings/net/renesas,*.yaml
 F:	drivers/net/ethernet/renesas/
 F:	include/linux/sh_eth.h
···
 M:	Binghui Wang <[e-mail]>
 L:	[e-mail]
 S:	Maintained
-F:	Documentation/devicetree/bindings/phy/phy-hi3660-usb3.txt
+F:	Documentation/devicetree/bindings/phy/hisilicon,hi3660-usb3.yaml
 F:	drivers/phy/hisilicon/phy-hi3660-usb3.c
 
 USB ISP116X DRIVER

drivers/staging/wfx/Documentation/devicetree/bindings/net/wireless/silabs,wfx.yaml

···
     In addition, it is recommended to declare a mmc-pwrseq on SDIO host above
     WFx. Without it, you may encounter issues with warm boot. The mmc-pwrseq
     should be compatible with mmc-pwrseq-simple. Please consult
-    Documentation/devicetree/bindings/mmc/mmc-pwrseq-simple.txt for more
+    Documentation/devicetree/bindings/mmc/mmc-pwrseq-simple.yaml for more
     information.
 
   For SPI':'