ARM: dts: imx23: Fix the gpmi/gpmi-nand DT name

Replace "gpmi" with "gpmi-nand" to get the
GPMI interface probing with DT instead of
failing to get clock.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Detlev Zundel <dzu@denx.de>
CC: Dong Aisheng <b29396@freescale.com>
CC: Fabio Estevam <fabio.estevam@freescale.com>
Cc: Linux ARM kernel <linux-arm-kernel@lists.infradead.org>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Wolfgang Denk <wd@denx.de>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>