hpet: remove useless check if fixmem32 is NULL

fixmem32 is assigned to address of res->data member
so the address is always valid

Actually since we are not checking for res != NULL
static analyzing is complaining about referencing the pointer
and consequent check for null.
The code snippet looks confusing also for human eyes.

Cc: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>