msm: kgsl: Fix datatype of count in kgsl_alloc_secure_pages

Change the data type of count in kgsl_alloc_secure_pages to
correctly handle the errors from kgsl_pool_alloc_pages.

Change-Id: Ib24c351304ab864d5884be8f8bddc7f74a487031
Signed-off-by: Harshitha Sai Neelati <hsaine@codeaurora.org>