s390/fpu: Re-add exception handling in load_fpu_state()
In the Linux kernel, the following vulnerability has been resolved:

s390/fpu: Re-add exception handling in load_fpu_state()

With the recent rewrite of the fpu code exception handling for the
lfpc instruction within load_fpu_state() was erroneously removed.

Add it again to prevent that loading invalid floating point register
values cause an unhandled specification exception.