crypto: nx - Rename devdata_mutex to devdata_spinlock

Rename devdata_mutex to devdata_spinlock to accurately reflect its
implementation as a spinlock.

[1] v1 https://lore.kernel.org/all/ZwyqD-w5hEhrnqTB@linux.ibm.com



Signed-off-by: Vishal Chourasia <vishalc@linux.ibm.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>