Ummm... a little more effort is needed.
Replace 'magic' number to named constant.
MOV DYTA,#8

is rewritten to
MAX_PACKET_SIZE EQU 8
MOV DYTA, #MAX_PACKET_SIZE

bLength                 EQU 30H
bDescriptorType         EQU 31H
bcdUSBH                 EQU 32H
bcdUSBL                 EQU 33H
bDeviceClass            EQU 34H
bDeviceSubclass         EQU 35H
bDeviceProtocol         EQU 36H
bMaxPacketSize          EQU 37H
idVendorH               EQU 38H
idVendorL               EQU 39H
idProductH              EQU 3AH
idProductL              EQU 3BH
bcdDeviceH              EQU 3CH
bcdDeviceL              EQU 3DH
iManufacture            EQU 3EH
iProducts               EQU 3FH
iSerialNumber           EQU 40H
bNumConfigurations      EQU 41H

As you see i have put an equ for bMaxPacketSize
When R0=30h bLength is sent and when it is 37h bMaxPacketSize
is sent,
mov DYTA,#8 that you have mentioned is extera byte for explaining the size of any piece of descriptor
Best Wishes
Mehdi