musb: Use name based initialization for musb_config

Changed musb_config initialization for omap3.c, davinci.c
and da8xx.c using name of structure fields. This would cause
the uninitialized field to be null by default and thus would
help in avoiding to init some flags required to be set only
for a few selected platforms.

CC: Remy Bohmer <linux@bohmer.net>
Signed-off-by: Ajay Kumar Gupta <ajay.gupta@ti.com>