OMAP: sDMA: Correct the the omap_request_dma_chain() signature

Original OMAP DMA chaining design has chain_id as one of the callback
parameters. The below patch broke the desing.
http://git.omapzoom.org/?p=repo/omapkernel.git;a=commitdiff;h=538528de0cb256f65716ab2e9613d9e920f97fe2
Now callback returns logical channel number and not chain_id.
Hence the signature of the omap_request_dma_chain() functions needs to be
corrected to avoid any confusion.

More details are on this email thread :
http://marc.info/?l=linux-omap&m=122961071931459&w=2

Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>