msm: ipa: change IPA_EVENT_MAX to better definition

IPA_EVENT_MAX represents the number of events that IPA supports for
ipa messaging interface. Currently IPA driver supports only WLAN events.
Fix the definition of IPA_EVENT_MAX to support more event types.

Change-Id: Ia2008408d7d4e5f90ceff8885768afd0af3f027b
Acked-by: Ady Abraham <adya@qti.qualcomm.com>
Signed-off-by: Gidon Studinski <gidons@codeaurora.org>