s390/sclp: Add check for get_zeroed_page()

In the Linux kernel, the following vulnerability has been resolved:

s390/sclp: Add check for get_zeroed_page()

Add check for the return value of get_zeroed_page() in

sclp_console_init() to prevent null pointer dereference.

Furthermore, to solve the memory leak caused by the loop

allocation, add a free helper to do the free job.