iwlwifi: mvm: make sure FW contains the right amount of paging sections

Paging contains 3 sections in the fw. The first for the paging separator,
The second for the CSS block, the third with the paging data.

Currently if the driver finds the paging separator, and there is only
section left (CSS), once reading the CSS section, the driver will
attempt to read the paging data and will go out of the arrays bounds.

Make sure that the FW image contains the right amount of sections for
paging.

Signed-off-by: Matti Gottlieb <matti.gottlieb@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>