msm: mhi_dev: update NHWER after M0 from host

Host might update NHWER value before issuing M0 to device.
So, update number of HW event rings after M0 is received from host.

Change-Id: I2e0b28a82e299e66b0167977c4c4ed9d7b6c889e
Signed-off-by: Rama Krishna Phani A <rphani@codeaurora.org>