ARM: 6174/1: ep93xx: clear devcfg bits before setting them

The ep93xx core helper function ep93xx_devcfg_set_clear should mask the
clear_bits before setting the new set_bits in case the clear_bits are a
mask value that also includes the set_bits.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Acked-by: Ryan Mallon <ryan@bluewatersys.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>