cfi_flash: fix flash on BE machines with CFG_WRITE_SWAPPED_DATA

This got broken by commits 93c56f21
 [cfi_flash: support of long cmd in U-boot.]

That command needs to be in little endian format on BE machines
with CFG_WRITE_SWAPPED_DATA. Without this patch, the command 0xf0
gets saved on stack as 0x00 00 00 f0 and 0x00 gets written into
the cmdbuf in case portwidth = chipwidth = 8bit.

Cc: Alexey Korolev <akorolev@infradead.org>
Cc: Vasiliy Leonenko <vasiliy.leonenko@mail.ru>
Signed-off-by: Sebastian Siewior <bigeasy@linutronix.de>