longlong to long long because MYSQL_SYSVAR_LONGLONG marco expects long long
type.

Also change
((ulint)innobase_buffer_pool_size) / 1024
to
(ulint)(innobase_buffer_pool_size / 1024)
and remove comment which is no longer true.

Provided that innobase_buffer_pool_size is always 64bits these statements
are equivalent if ulint is 64 bit (well it will screw up if
innobase_buffer_pool_size is negative). And if ulint is 32 bit the later
variant gives a little more chance that the value will fit.

Approved by:	Heikki