spi/omap: Remove bus_num usage for instance index

bus_num was used to reference the mcspi controller instance in a fixed array.
Remove this array and store this information directly inside drvdata structure.

bus_num is now just set if the pdev->id is present or with -1 for dynamic
allocation by SPI core, but the driver does not access it anymore.

Clean some bad comments format, and remove un-needed space.

Signed-off-by: Benoit Cousson <b-cousson@ti.com>
[Cleanup the OMAP2_MCSPI_MAX_CTRL macro as it is not needed anymore]
Signed-off-by: Shubhrajyoti D <shubhrajyoti@ti.com>