platform/x86: thinkpad_acpi: use strstarts()

There is a function, `strstarts()`, in linux/string.h
to check if a string is prefix of another. So remove
the custom version from the driver.

Signed-off-by: Barnabás Pőcze <pobrn@protonmail.com>
Link: https://lore.kernel.org/r/20221021180007.55535-1-pobrn@protonmail.com


Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>