PNP: isapnp: remove defined but not used function 'isapnp_checksum'

PNP: isapnp: remove defined but not used function 'isapnp_checksum'

Fix gcc '-Wunused-function' warnning:

drivers/pnp/isapnp/core.c:752:29: warning: 'isapnp_checksum' defined but
not used [-Wunused-function]
752 | static unsigned char __init isapnp_checksum(unsigned char *data)

Commit 41055569a36c ("PNP: isapnp: remove set but not used variable
'checksum'") removes the last caller of the function. It is never used
and so can be removed.

Fixes: 41055569a36c ("PNP: isapnp: remove set but not used variable 'checksum'")
Signed-off-by: yu kuai <yukuai3@huawei.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>