[POWERPC] QE: Rename ucc_slow_info.us_regs to ucc_slow_info.regs

Rename the 'us_regs' field of the ucc_slow_info structure in ucc_slow.h
to just 'regs'.  The equivalent field in the ucc_fast_info structure is
also called 'regs', so this patch makes them comparable, and makes the
code a little easier to read, because there already is a 'us_regs' in
another ucc_slow structure.

Signed-off-by: Timur Tabi <timur@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>