OMAP2+: mux: fix compilation warnings

Fix below compilation warnings.

arch/arm/mach-omap2/omap_hwmod.c: In function 'omap_hwmod_for_each':
arch/arm/mach-omap2/omap_hwmod.c:1631: warning: 'ret' may be used uninitialized in this function

arch/arm/mach-omap2/mux.c: In function 'omap_mux_get_gpio':
arch/arm/mach-omap2/mux.c:917: warning: 'm' may be used uninitialized in this function

Signed-off-by: Govindraj.R <govindraj.raja@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>