char: hpet: add checks after calling ioremap

The function hpet_resources() calls ioremap() two times, but in both
cases it does not check if ioremap() returned a null pointer. Fix this
by adding null pointer checks and returning an appropriate error.

Signed-off-by: Tom Seewald <tseewald@gmail.com>
Link: https://lore.kernel.org/r/20210503115736.2104747-30-gregkh@linuxfoundation.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>