mwifiex: remove misleading GFP_DMA flag in buffer allocations

The GFP_DMA flag is obviously misunderstood in the mwifiex driver. It's
meant for legacy ISA DMA memory mappings only -- the lower 16MB on x86.
That doesn't apply to PCIe or SDIO devices, I guess.

Remove the GFP_DMA flag to reduce the need to place the socket buffer
allocation into the low mem DMA area, which might already be in use by
other drivers.

This misuse was flagged by the PaX USERCOPY feature by chance, as it
detected the user copy operation from a DMA buffer in the recvfrom()
syscall path.

Signed-off-by: Mathias Krause <minipli@googlemail.com>
Tested-by: Dennis Wassenberg <dennis.wassenberg@secunet.com>
Cc: Amitkumar Karwar <akarwar@marvell.com>
Cc: Nishant Sarmukadam <nishants@marvell.com>
Cc: Xinming Hu <huxm@marvell.com>
Cc: Kalle Valo <kvalo@codeaurora.org>
Cc: Brad Spengler <spender@grsecurity.net>
Cc: PaX Team <pageexec@freemail.hu>
Acked-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>