ecryptfs: Replace strcpy with strscpy in ecryptfs_cipher_code_to_string

ecryptfs: Replace strcpy with strscpy in ecryptfs_cipher_code_to_string

strcpy() has been deprecated [1] because it performs no bounds checking
on the destination buffer, which can lead to buffer overflows. Since
the parameter 'char *str' is just a pointer with no size information,
extend the function with a 'size' parameter to pass the destination
buffer's size as an additional argument. Adjust the call sites
accordingly.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strcpy
Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Signed-off-by: Tyler Hicks <code@tyhicks.com>