pca9468_charger: Add misisng fallthrough

This fixes build issues which requires switch cases without a break to
explicitly include a "fallthrough" statement.

Bug: 288966302
Fixes: d8456dec9a74 ("P22: Enable dynamic IR drop")
Change-Id: I0f9dcc554824062b72bbbf2ebf4123ceed3c836d
Signed-off-by: Will McVicker <[email protected]>
1 file changed