NTB: ntb_perf: fix cast to restricted __le32

Sparse is whining about the u32 and __le32 mixed usage in the driver

drivers/ntb/test/ntb_perf.c:288:21: warning: cast to restricted __le32
drivers/ntb/test/ntb_perf.c:295:37: warning: incorrect type in argument 4 (different base types)
drivers/ntb/test/ntb_perf.c:295:37:    expected unsigned int [unsigned] [usertype] val
drivers/ntb/test/ntb_perf.c:295:37:    got restricted __le32 [usertype] <noident>
...

NTB hardware drivers shall accept CPU-endian data and translate it to
the portable formate by internal means, so the explicit conversions
are not necessary before Scratchpad/Messages API usage anymore.

Fixes: b83003b3fdc1 ("NTB: ntb_perf: Add full multi-port NTB API support")
Signed-off-by: Serge Semin <fancer.lancer@gmail.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Jon Mason <jdmason@kudzu.us>