s390/facilities: Fix warning about shadow of global variable

Compiling the kernel with clang W=2 produces a warning that the
parameter declarations in some routines would shadow the definition of
the global variable stfle_fac_list. Address this warning by renaming the
parameters to fac_list.

Fixes: 17e89e13 ("s390/facilities: move stfl information from lowcore to global data")
Signed-off-by: Gerd Bayer <gbayer@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>