docs: ABI: fixed req_number desc in UAC1

Fixed wording of the req_number description in UAC1 docs.
Signed-off-by: Pavel Hofman <pavel.hofman@ivitera.com>
Link: https://lore.kernel.org/r/20211225130929.205629-2-pavel.hofman@ivitera.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/ABI/testing/configfs-usb-gadget-uac1

@@ -27,6 +27,6 @@ Description:
 					(in 1/256 dB)
 		p_volume_res		playback volume control resolution
 					(in 1/256 dB)
-		req_number		the number of pre-allocated request
+		req_number		the number of pre-allocated requests
 					for both capture and playback
 		=====================	=======================================

Documentation/usb/gadget-testing.rst

@@ -931,7 +931,7 @@ The uac1 function provides these attributes in its function directory:
 	p_volume_min     playback volume control min value (in 1/256 dB)
 	p_volume_max     playback volume control max value (in 1/256 dB)
 	p_volume_res     playback volume control resolution (in 1/256 dB)
-	req_number       the number of pre-allocated request for both capture
+	req_number       the number of pre-allocated requests for both capture
 	                 and playback
 	================ ====================================================