sh: tmu: Simplify the tmu_bit math

The tmu_bit value evaluates to (ffs(4) >> 1) - 1 = (3 >> 1) - 1 = 0.
Just drop the tmu_bit completely as well as CONFIG_SYS_TMU_CLK_DIV.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>