dt-bindings: mfd: bd9571mwv: update rohm,bd9571mwv.yaml reference

Changeset 983b6297 ("dt-bindings: mfd: bd9571mwv: Convert to json-schema")
renamed: Documentation/devicetree/bindings/mfd/bd9571mwv.txt
to: Documentation/devicetree/bindings/mfd/rohm,bd9571mwv.yaml.

Update its cross-reference accordingly.

Fixes: 983b6297 ("dt-bindings: mfd: bd9571mwv: Convert to json-schema")
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/1906a4d935eab57c10ce09358eae02175ce4abb7.1654529011.git.mchehab@kernel.org

Documentation/ABI/testing/sysfs-driver-bd9571mwv-regulator

@@ -26,6 +26,6 @@ Description:	Read/write the current state of DDR Backup Mode, which controls
 		     DDR Backup Mode must be explicitly enabled by the user,
 		     to invoke step 1.
 
-		See also Documentation/devicetree/bindings/mfd/bd9571mwv.txt.
+		See also Documentation/devicetree/bindings/mfd/rohm,bd9571mwv.yaml.
 Users:		User space applications for embedded boards equipped with a
 		BD9571MWV PMIC.