i2c: nomadik: simplify IRQ masking logic

IRQ_MASK and I2C_CLEAR_ALL_INTS both mask available interrupts. IRQ_MASK
removes top options (bits 29-31). I2C_CLEAR_ALL_INTS removes reserved
options including top bits. Keep the latter.

31  29  27  25  23  21  19  17  15  13  11  09  07  05  03  01
  30  28  26  24  22  20  18  16  14  12  10  08  06  04  02  00
-- IRQ_MASK: ---------------------------------------------------
      1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
0 0 0
-- I2C_CLEAR_ALL_INTS: -----------------------------------------
      1     1 1       1 1 1 1 1                   1 1 1 1 1 1 1
0 0 0   0 0     0 0 0           0 0 0 0 0 0 0 0 0

Notice I2C_CLEAR_ALL_INTS is more restrictive than IRQ_MASK.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Andi Shyti <andi.shyti@kernel.org>
Signed-off-by: Théo Lebrun <theo.lebrun@bootlin.com>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>