July 31 (Reuters) - Memory chipmaker Western Digital Corp (WDC.O) forecast first-quarter revenue below Wall Street targets and a bigger-than-expected loss on Monday as weak demand, particularly for its cloud business, forces it to cut production. The company said it expects its current-quarter loss to include a charge of about $200 million to $220 million for underutilization of its factories. Western Digital forecast its adjusted loss per share to be in the range of $2.10 to $1.80, compared to an estimated loss of $1.40 per share. It also forecast revenue for the same period below estimates. Excess inventory clearance in...