net: page_pool: fix warning code

WARN_ON_ONCE("string") doesn't really do what appears to
be intended, so fix that.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Fixes: 90de47f0 ("page_pool: fragment API support for 32-bit arch with 64-bit DMA")
Link: https://patch.msgid.link/20240705134221.2f4de205caa1.I28496dc0f2ced580282d1fb892048017c4491e21@changeid


Signed-off-by: Jakub Kicinski <kuba@kernel.org>