hashmap_entry_init takes "struct hashmap_entry *"

hashmap_entry_init takes "struct hashmap_entry *"

C compilers do type checking to make life easier for us.  So
rely on that and update all hashmap_entry_init callers to take
"struct hashmap_entry *" to avoid future bugs while improving
safety and readability.

Signed-off-by: Eric Wong <redacted>
Reviewed-by: Derrick Stolee <redacted>
Signed-off-by: Junio C Hamano <redacted>