mhi: core: Fix format specifier in mhi_alloc_bhie_table

BHIe table size is printed incorrectly as unsigned long.
size is of type size_t hence use %zu instead of %lu.

Change-Id: Ic52bc6ea92e6dac8bd1e275f9a17986d08e2da79
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>