Finish basic updates to let the DaVinci MMC driver talk to
the second MMC controller on dm355:

 - Update the MMC driver to use clk_get() correctly
    * use logical "mmc" clockname
    * fix its error handling logic (!)

 - Bugfixes to probe():
    * call mmc_add_host() only *after* everything is set up
    * check for mmc_add_host() errors
    * call request_irq() only after the host was added
    * start timer polling only after the host was added

 - And some cosmetic bits:
    * use more modern timer setup calls
    * request_irq() says mmc0 or mmc1, matching custom

So now it comes up on both MMC controllers, and starts collecting
interrupts on the second ... so there's progress.  But it can't
see a card in either slot of a dm355 yet.
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>