ARM: tegra: rename MASK_BITS_29_28 to MASK_BITS_31_28

ARM: tegra: rename MASK_BITS_29_28 to MASK_BITS_31_28

The only place where the MASK_BITS_* values are used is in
adjust_periph_pll(), which interprets the value 4 (old MASK_BITS_29_28,
new MASK_BITS_31_28) as being associated with mask OUT_CLK_SOURCE4_MASK,
i.e. bits 31:28. Rename the MASK_BITS_ macro to reflect how it's actually
implemented.

Note that no Tegra clock register actually uses all of bits 31:28 as
the mux field. Rather, bits 30:28, 29:28, or 28 are used. However, in
those cases, nothing is stored in the bits above the mux field, so it's
safe to pretend that the mux field extends all the way to the end of the
register. As such, the U-Boot clock driver is currently a bit lazy, and
doesn't distinguish between 31:28, 30:28, 29:28 and 28; it just lumps
them all together and pretends they're all 31:28. This patch doesn't
cause this issue; it was pre-existing. Hopefully, future patches will
clean this up.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Reviewed-by: Thierry Reding <treding@nvidia.com>
Tested-by: Thierry Reding <treding@nvidia.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Tom Warren <twarren@nvidia.com>