Fix flock name for gen-initramfs lock as $(2) starts with .HASH making
the lock name gen-initramfs-.HASH.flock
Fix this to a better name of gen-initramfs.HASH.flock
Fixes: 52cc9d82f1 ("kernel: rework Initramfs locking logic")
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>