msm: Warning fix in trout gpio board file

arch/arm/mach-msm/board-trout-gpio.c: In function 'trout_gpio_to_irq':
arch/arm/mach-msm/board-trout-gpio.c:77: error: unused variable 'msm_gpio'

Signed-off-by: David Brown <davidb@codeaurora.org>