s390/cio: make sch->lock spinlock pointer a member

s390/cio: make sch->lock spinlock pointer a member

The lock member of struct subchannel used to be a spinlock, but became
a pointer to a spinlock with commit 2ec2298412e1 ("[S390] subchannel
lock conversion."). This might have been justified back then, but with
the current state of affairs, there is no reason to manage a separate
spinlock object.

Let's simplify things and pull the spinlock back into struct subchannel.

Signed-off-by: Halil Pasic <pasic@linux.ibm.com>
Reviewed-by: Vineeth Vijayan <vneethv@linux.ibm.com>
Link: https://lore.kernel.org/r/20231101115751.2308307-1-pasic@linux.ibm.com
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>