clk: ux500: fix bit error

This fixes a bit error in the U8500 clock implementation: the
unused p2_pclk12 registered at bit 12 in periphereral group 6
was defined as using bit 11 rather than bit 12.

When walking over and disabling the unused clocks in the tree
at late init time, p2_pclk12 was disabled, by effectively
clearing the but for p2_pclk11 instead of bit 12 as it should
have, thus disabling gpio block 6 and 7.

Reported-by: Lee Jones <lee.jones@linaro.org>
Acked-by: Ulf Hansson <ulf.hansson@linaro.org>
Cc: Philippe Begnic <philippe.begnic@st.com>
Cc: stable@kernel.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Mike Turquette <mturquette@linaro.org>