misc: pci_endpoint_test: Aggregate params checking for xfer

Each transfer test functions have same parameter checking code. This patch
unites those to an introduced function.

Signed-off-by: Shunsuke Mie <mie@igel.co.jp>
Cc: stable <stable@kernel.org>
Link: https://lore.kernel.org/r/20220907020100.122588-1-mie@igel.co.jp


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