Initialize pagesize_m1 in bfd_cache_init

Initialize pagesize_m1 in bfd_cache_init

There is no need to check and initialize pagesize_m1 in cache_bmmap.

	* cache.c (cache_bmmap): Move pagesize_m1 ... to
	(pagesize_m1): Here.
	(bfd_cache_init): Initialize pagesize_m1.