MAINTAINERS: Remove Hemant from MHI bus

Hemant moved out of Qualcomm and expressed his wish to not continue doing
any reviews for MHI patches. So let's remove him from MAINTAINERS file.

Reviewed-by: Jeffrey Hugo <quic_jhugo@quicinc.com>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>