msm: ipa: cap ipa rx buffer pool size

This check ensures that we don't dimension the pool to be
larger than the descriptor FIFO (whose size is client
specified) permits.

Change-Id: Ib0224af1e3008fd9e81412aca65dc72770392685
Signed-off-by: Ravi Gummadidala <rgummadi@codeaurora.org>