PrioritizedQueue.h: pass 'K' by reference to enqueue*()

Fix for:

CID 745921 (#1 of 1): Big parameter passed by value (PASS_BY_VALUE)
 pass_by_value: Passing parameter cl of type entity_inst_t (size
 152 bytes) by value.

CID 745922 (#1 of 1): Big parameter passed by value (PASS_BY_VALUE)
 pass_by_value: Passing parameter cl of type entity_inst_t (size
 152 bytes) by value.

CID 745923 (#1 of 1): Big parameter passed by value (PASS_BY_VALUE)
 pass_by_value: Passing parameter cl of type entity_inst_t (size
 152 bytes) by value.

CID 745924 (#1 of 1): Big parameter passed by value (PASS_BY_VALUE)
 pass_by_value: Passing parameter cl of type entity_inst_t (size
 152 bytes) by value.

CID 745925 (#1 of 1): Big parameter passed by value (PASS_BY_VALUE)
 pass_by_value: Passing parameter cl of type entity_inst_t (size
 152 bytes) by value.

CID 745926 (#1 of 1): Big parameter passed by value (PASS_BY_VALUE)
 pass_by_value: Passing parameter cl of type entity_inst_t (size
 152 bytes) by value.

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>