ASoC: adau1372: Fix error handling in adau1372_set_power()

ASoC: adau1372: Fix error handling in adau1372_set_power()

Jihed Chaibi <jihed.chaibi.dev@gmail.com> says:

adau1372_set_power() had two related error handling issues in its enable
path: clk_prepare_enable() was called but its return value discarded, and
adau1372_enable_pll() was a void function that silently swallowed lock
failures, leaving mclk enabled and adau1372->enabled set to true despite
the device being in a broken state.

Patch 1 fixes the unchecked clk_prepare_enable() by making
adau1372_set_power() return int and propagating the error.

Patch 2 converts adau1372_enable_pll() to return int and adds a full
unwind in adau1372_set_power() if PLL lock fails, reversing the regcache,
GPIO power-down, and clock state.