wlcore: fix 64K page support

wlcore: fix 64K page support

commit 4a4274bf2dbbd1c7a45be0c89a1687c9d2eef4a0 upstream.

In the stable linux-3.16 branch, I ran into a warning in the
wlcore driver:

drivers/net/wireless/ti/wlcore/spi.c: In function 'wl12xx_spi_raw_write':
drivers/net/wireless/ti/wlcore/spi.c:315:1: error: the frame size of 12848 bytes is larger than 2048 bytes [-Werror=frame-larger-than=]

Newer kernels no longer show the warning, but the bug is still there,
as the allocation is based on the CPU page size rather than the
actual capabilities of the hardware.

This replaces the PAGE_SIZE macro with the SZ_4K macro, i.e. 4096 bytes
per buffer.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
[bwh: Backported to 3.2:
 - Open-code SZ_4K as it is only defined on some architectures here(!)
 - Adjust filename, context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>