ARM: omap2: gpmc: Remove redundant chip select out of range check

This check is done before the call to gpmc_cs_reserved() and
gpmc_cs_set_reserved() and it's redundant to do it again in each
function. This simplifies the code a bit.

Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Reviewed-by: Jon Hunter <jon-hunter@ti.com>
Signed-off-by: Jon Hunter <jon-hunter@ti.com>