ARM: OMAP2+: gpmc: Don't complain if wait pin is used without r/w monitoring

For NAND read & write wait pin monitoring must be kept disabled as the
wait pin is only used to indicate NAND device ready status and not to
extend each read/write cycle.

So don't print a warning if wait pin is specified while read/write
monitoring is not in the device tree.

Sanity check wait pin number irrespective if read/write monitoring is
set or not.

Signed-off-by: Roger Quadros <rogerq@ti.com>
Reviewed-by: Pekon Gupta <pekon@pek-sem.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>