spi: omap2-mcspi: Fix the below warning

The dma_map and dma_unmap should have same parameter
passed otherwise we get the below warn.

ks8851 spi1.0: DMA-API: device driver tries to free DMA memory it has not allocated [device address=0x000000009f22]

[    2.066925] Modules linked in:
[    2.070312]
[    2.071929] [<c001c250>] (unwind_backtrace+0x0/0x130) from [<c0043d84>] (warn_slowpath_common+0x4c/0x64)
[    2.081909] [<c0043d84>] (warn_slowpath_common+0x4c/0x64) from [<c0043e30>] (warn_slowpath_fmt+0x30/0x40)
[    2.091949] [<c0043e30>] (warn_slowpath_fmt+0x30/0x40) from [<c0293824>] (check_unmap+0x6d0/0x7b0)
[    2.101348] [<c0293824>] (check_unmap+0x6d0/0x7b0) from [<c02939cc>] (debug_dma_unmap_page+0x64/0x70)
[    2.111053] [<c02939cc>] (debug_dma_unmap_page+0x64/0x70) from [<c03519a4>] (omap2_mcspi_txrx_dma+0x2d8/0x4fc)
[    2.121582] [<c03519a4>] (omap2_mcspi_txrx_dma+0x2d8/0x4fc) from [<c03524d8>] (omap2_mcspi_work.clone.4+0xf0/0x290)
[    2.132537] [<c03524d8>] (omap2_mcspi_work.clone.4+0xf0/0x290) from [<c0352900>] (omap2_mcspi_transfer_one_message+0x288/0x438)
[    2.144592] [<c0352900>] (omap2_mcspi_transfer_one_message+0x288/0x438) from [<c03503bc>] (spi_pump_messages+0x100/0x160)
[    2.156127] [<c03503bc>] (spi_pump_messages+0x100/0x160) from [<c006635c>] (kthread_worker_fn+0xac/0x180)
[    2.166168] [<c006635c>] (kthread_worker_fn+0xac/0x180) from [<c0066578>] (kthread+0x90/0x9c)
[    2.175140] [<c0066578>] (kthread+0x90/0x9c) from [<c00157fc>] (kernel_thread_exit+0x0/0x8)
[    2.183898] ---[ end trace d1830ce6e44292f2 ]---

Fix the warn by changing the unmap parameter.

Reported-by: Russell King - ARM Linux <linux@arm.linux.org.uk>
Signed-off-by: Shubhrajyoti D <shubhrajyoti@ti.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>