page_pool: fix documentation typos

Correct grammar for better readability.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Jesper Dangaard Brouer <hawk@kernel.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Acked-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Link: https://lore.kernel.org/r/20231001003846.29541-1-rdunlap@infradead.org


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