msm: mhi_dev: Increase size of ipa_clnt_hndl array

ipa_clnt_hndl array supports only 4 channels. Few targets can
support more MHI HW channels and can cause out of bound access
for higher MHI channels.

Increase ipa_clnt_hndl array size to accommodate the maximum
number of supported MHI HW channels.

Change-Id: Ifb4b17c40a7ac690b9a7fd864b7eb0ade2e5de43
Signed-off-by: Nitesh Gupta <nitegupt@codeaurora.org>