Change Item Quantity on Equip

# change the item quantity in the inventory
# Parameters:
#   r4 = Item Number
#   r5 = Value
# 
# Return Value:
#   item quantity

001208b8: 308403ff andi r4,r4,0x03ff           # 
001208bc: 1080000c beq r4,r0,0x001208f0        # if item number AND 0x3FF = 0
001208c0: 00001021 addu r2,r0,r0			    #   return 0
001208c4: 3c018006 lui r1,0x8006               #
001208c8: 00240821 addu r1,r1,r4               #
001208cc: 902296e0 lbu r2,-0x6920(r1)          # item quantity = inventory[item number]
001208d0: 00000000 nop                         #
001208d4: 00451021 addu r2,r2,r5               # item quantity += value
001208d8: 04410002 bgez r2,0x001208e4          # if item quantity is negative:
001208dc: 00000000 nop                         #
001208e0: 00001021 addu r2,r0,r0               #   item quantity = 0
001208e4: 3c018006 lui r1,0x8006               #
001208e8: 00240821 addu r1,r1,r4               #
001208ec: a02296e0 sb r2,-0x6920(r1)           # inventory[item number] = item quantity
001208f0: 03e00008 jr r31                      # return item quantity
001208f4: 00000000 nop                         #