Fix booting on ARM.
Fix booting on ARM.

In PHYS_TO_VM_PAGE() when VM_PHYSSEG_DENSE is set the check if we are past
the end of vm_page_array was incorrect causing it to return NULL. This
value is then used in vm_phys_add_page causing a data abort.

Reviewed by:	alc, kib, imp
Tested by:	stas

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