ARM: dts: omap4-droid4: Allow 300mA current for USB peripherals

Looks like we can use some USB Ethernet dongles for example if we increase
the allowed power limit.

A similar PMIC MC13783 documents maximum current limit as 300 mA in in
"Table 10-4. VBUS Regulator Main Characteristics". Since we have no
other documentation, let's use that value as the limit.

Cc: Jacopo Mondi <jacopo@jmondi.org>
Cc: Marcel Partap <mpartap@gmx.net>
Cc: Merlijn Wajer <merlijn@wizzup.org>
Cc: Michael Scott <hashcode0f@gmail.com>
Cc: NeKit <nekit1000@gmail.com>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Sebastian Reichel <sre@kernel.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>