ARM: dts: Fix am33xx.dtsi USB ranges length

AM335x TRM: Table 2-1 defines USBSS - USB Queue Manager in memory region
0x4740 0000 to 0x4740 7FFF.

Looks like the older TRM revisions list the range from 0x5000 to 0x8000
as reserved.

Fixes: 0782e857 ("ARM: dts: Probe am335x musb with ti-sysc")
Signed-off-by: Oskar Holmlund <oskar@ohdata.se>
[tony@atomide.com: updated comments]
Signed-off-by: Tony Lindgren <tony@atomide.com>